Revert "Silence Clang -Werror,-Wreturn-type-c-linkage"

This reverts commit f14cedc4, now that
66791053 reverted
9f016bd6 again.

solenv/gbuild/platform/com_GCC_defs.mk

@@ -72,14 +72,6 @@ gb_CXXFLAGS_COMMON := \
 	-fno-common \
 	-pipe \
 
-# VCL_BUILDER_DECL_FACTORY (include/vcl/builderfactory.hxx) routinely causes
-# "'make...' has C-linkage specified, but returns user-defined type
-# 'VclPtr<vcl::Window>' which is incompatible with C
-# [-Werror,-Wreturn-type-c-linkage]":
-ifeq ($(COM_GCC_IS_CLANG),TRUE)
-gb_CXXFLAGS_COMMON += -Wno-return-type-c-linkage
-endif
-
 gb_CXXFLAGS_Wundef = -Wno-undef
 
 ifneq ($(HAVE_THREADSAFE_STATICS),TRUE)