exernal/icu: Various C++20 comparison operator fixes

There are three patterns here:

* Missing const (source/common/uvector.cpp, source/common/uvector.h):  Overload
resolution ambiguities when a synthesized canditate of operator == for a
reversed-argument rewrite conflicts with the actual operator ==, due to the
asymmetric const-ness of the implicit object parameter and the RHS parameter:

> uniset.cpp:360:18: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::UVector' and 'icu_63::UVector')
>     if (*strings != *o.strings) return FALSE;
>         ~~~~~~~~ ^  ~~~~~~~~~~
> ./uvector.h:385:23: note: candidate function
> inline UBool UVector::operator!=(const UVector& other) {
>                       ^
> ./uvector.h:116:11: note: candidate function
>     UBool operator==(const UVector& other);
>           ^
> ./uvector.h:116:11: note: candidate function (with reversed parameter order)

* UBool -> bool (source/i18n/tzrule.cpp, source/i18n/unicode/tzrule.h):
[over.match.oper]/9 (of the current C++20 draft) states:  "If a rewritten
operator== candidate is selected [...], its return type shall be cv bool":

> basictz.cpp:411:37: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '==' comparison is not 'bool'
>                 if (*(tzt0.getTo()) == *tar) {
>                     ~~~~~~~~~~~~~~~ ^  ~~~~
> ./unicode/tzrule.h:675:19: note: declared here
>     virtual UBool operator==(const TimeZoneRule& that) const;
>                   ^

* Additional operator != (source/i18n/unicode/rbtz.h,
source/i18n/unicode/simpletz.h, source/i18n/unicode/smpdtfmt.h,
source/i18n/unicode/stsearch.h, source/i18n/unicode/tzrule.h,
source/i18n/unicode/vtzone.h):  Similar to the previous pattern, but here the
original operator used was !=, so an alternative fix (that reqires fewer
changes to the code overall) is to add specific operator != overloads:

> rbtz.cpp:79:15: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::RuleBasedTimeZone' and 'const icu_63::RuleBasedTimeZone')
>     if (*this != right) {
>         ~~~~~ ^  ~~~~~
> ./unicode/rbtz.h:87:19: note: candidate function
>     virtual UBool operator!=(const TimeZone& that) const;
>                   ^
> ./unicode/rbtz.h:77:19: note: candidate function
>     virtual UBool operator==(const TimeZone& that) const;
>                   ^
> ./unicode/rbtz.h:77:19: note: candidate function (with reversed parameter order)
> rbtz.cpp:101:23: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::InitialTimeZoneRule' and 'icu_63::InitialTimeZoneRule')
>     if (*fInitialRule != *(rbtz->fInitialRule)) {
>         ~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~~
> ./unicode/tzrule.h:257:19: note: candidate function
>     virtual UBool operator!=(const TimeZoneRule& that) const;
>                   ^
> ./unicode/tzrule.h:248:18: note: candidate function
>     virtual bool operator==(const TimeZoneRule& that) const;
>                  ^
> ./unicode/tzrule.h:248:18: note: candidate function (with reversed parameter order)
> rbtz.cpp:535:23: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::InitialTimeZoneRule' and 'icu_63::InitialTimeZoneRule')
>     if (*fInitialRule != *(that.fInitialRule)) {
>         ~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~~~
> ./unicode/tzrule.h:257:19: note: candidate function
>     virtual UBool operator!=(const TimeZoneRule& that) const;
>                   ^
> ./unicode/tzrule.h:248:18: note: candidate function
>     virtual bool operator==(const TimeZoneRule& that) const;
>                  ^
> ./unicode/tzrule.h:248:18: note: candidate function (with reversed parameter order)
>
> olsontz.cpp:630:69: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '!=' comparison is not 'bool'
>         || (finalZone != NULL && z->finalZone != NULL && *finalZone != *z->finalZone)) {
>                                                          ~~~~~~~~~~ ^  ~~~~~~~~~~~~~
> ./unicode/simpletz.h:112:19: note: declared here
>     virtual UBool operator==(const TimeZone& that) const;
>                   ^

> dtitvfmt.cpp:223:62: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '!=' comparison is not 'bool'
>         if (fDateFormat && fmt->fDateFormat && (*fDateFormat != *fmt->fDateFormat)) {return FALSE;}
>                                                 ~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~
> ./unicode/smpdtfmt.h:876:19: note: declared here
>     virtual UBool operator==(const Format& other) const;
>                   ^

> stsearch.cpp:187:17: error: return type 'UBool' (aka 'signed char') of selected 'operator==' function for rewritten '!=' comparison is not 'bool'
>     if ((*this) != that) {
>         ~~~~~~~ ^  ~~~~
> ./unicode/stsearch.h:299:19: note: declared here
>     virtual UBool operator==(const SearchIterator &that) const;
>                   ^

> vtzone.cpp:1003:15: error: use of overloaded operator '!=' is ambiguous (with operand types 'icu_63::VTimeZone' and 'const icu_63::VTimeZone')
>     if (*this != right) {
>         ~~~~~ ^  ~~~~~
> ./unicode/vtzone.h:83:19: note: candidate function
>     virtual UBool operator!=(const TimeZone& that) const;
>                   ^
> ./unicode/vtzone.h:73:19: note: candidate function
>     virtual UBool operator==(const TimeZone& that) const;
>                   ^
> ./unicode/vtzone.h:73:19: note: candidate function (with reversed parameter order)

Change-Id: I38e01143d1ea0df3f43de53303fd710e41bae027
Reviewed-on: https://gerrit.libreoffice.org/81306
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/external/icu/UnpackedTarball_icu.mk b/external/icu/UnpackedTarball_icu.mk
index d8a16e0e3777..4d45f2108f99 100644
--- a/external/icu/UnpackedTarball_icu.mk
+++ b/external/icu/UnpackedTarball_icu.mk
@@ -43,6 +43,7 @@ $(eval $(call gb_UnpackedTarball_add_patches,icu,\
 	external/icu/char8_t.patch \
 	external/icu/CVE-2018-18928.patch.2 \
 	external/icu/clang-cl.patch \
+	external/icu/c++20-comparison.patch \
 ))
 
 $(eval $(call gb_UnpackedTarball_add_file,icu,source/data/brkitr/khmerdict.dict,external/icu/khmerdict.dict))