avoid gbuild warning about no PCH for libcmis

gb_LinkTarget_set_precompiled_header sets PCH_CXXFLAGS, so add_cxxflags
must go after it.

Change-Id: I527906661dcecff56a24d5733bd87b4c9bf96215
Reviewed-on: https://gerrit.libreoffice.org/73000
Tested-by: Jenkins
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>

external/libcmis/StaticLibrary_libcmis.mk

@@ -11,6 +11,8 @@ $(eval $(call gb_StaticLibrary_StaticLibrary,libcmis))
 
 $(eval $(call gb_StaticLibrary_set_warnings_disabled,libcmis))
 
+$(eval $(call gb_StaticLibrary_set_precompiled_header,libcmis,$(SRCDIR)/external/libcmis/inc/pch/precompiled_libcmis))
+
 ifeq ($(COM_IS_CLANG),TRUE)
 # Avoid narrowing conversion error (even though the option is technically a warning)
 # caused by boost
@@ -23,8 +25,6 @@ $(eval $(call gb_StaticLibrary_add_defs,libcmis, \
 	-DBOOST_ALL_NO_LIB \
 ))
 
-$(eval $(call gb_StaticLibrary_set_precompiled_header,libcmis,$(SRCDIR)/external/libcmis/inc/pch/precompiled_libcmis))
-
 $(eval $(call gb_StaticLibrary_set_include,libcmis, \
     -I$(call gb_UnpackedTarball_get_dir,libcmis/inc) \
     -I$(call gb_UnpackedTarball_get_dir,libcmis/src/libcmis) \