gbuild: fix actually used libraries for mergelib

Just the $(filter $(gb_MERGEDLIBS),$(2)) in the "if" was wrong,
but reformat and add a comment to make the code easier to read.

This way we correctly header-depend on all requested libraries,
but just export-depend on the real libraries.

And actually use gb_LinkTarget__is_build_lib in the ifeq, as
otherwise the build now fails for the reduced dependencies.

Change-Id: I24d5701891324f5055c9dfa535bd854d09fbb905
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/127994
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

0 files changed, 0 insertions, 0 deletions