abort if PCH cannot be used because of CXXFLAGS mismatch

Those should mean an error somewhere, e.g. as in the recent libcmis fix.

Change-Id: Iecb973a8f1d56a1bfa0a0e8a5c923e5598682b94
Reviewed-on: https://gerrit.libreoffice.org/73029Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>
Tested-by: Jenkins

solenv/gbuild/LinkTarget.mk

@@ -273,9 +273,10 @@ ifneq ($(strip $$(PCH_NAME)),)
 ifeq ($$(sort $$(PCH_CXXFLAGS) $$(PCH_DEFS) $$(gb_LinkTarget_EXCEPTIONFLAGS)),$$(sort $$(T_CXXFLAGS) $$(T_CXXFLAGS_APPEND) $$(DEFS)))
 $$@ : PCHFLAGS := $$(call gb_PrecompiledHeader_get_enableflags,$$(PCH_NAME),$$(PCH_LINKTARGETMAKEFILENAME))
 else
-$$(info No precompiled header available for $$*.cxx .)
+$$(warning No precompiled header available for $$*.cxx .)
 $$(info precompiled header flags : $$(sort $$(PCH_CXXFLAGS) $$(PCH_DEFS) $$(gb_LinkTarget_EXCEPTIONFLAGS)))
 $$(info .           object flags : $$(sort $$(T_CXXFLAGS) $$(T_CXXFLAGS_APPEND) $$(DEFS)))
+$$(error   Incorrect precompiled header setup or internal gbuild error.)
 $$@ : PCHFLAGS :=
 endif
 endif