use full path for -include .gch

With just -include a.hxx ccache checks only for presence of a.hxx.gch
and it doesn't search the path given by -I, so it didn't detect the usage
of the .gch and thus didn't include it in the checksum, possibly leading
to false positives. Icecream similarly doesn't search paths given by -I
and may fail to properly handle the .gch usage.

Change-Id: I40ba2d5089e77cd5e8da670c7e030f9e90ebc8ac
Reviewed-on: https://gerrit.libreoffice.org/72703
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>

solenv/gbuild/platform/com_GCC_class.mk

@@ -82,8 +82,8 @@ ifeq ($(COM_IS_CLANG),TRUE)
 gb_PrecompiledHeader_get_enableflags = -include-pch $(call gb_PrecompiledHeader_get_target,$(1),$(2))
 gb_PrecompiledHeader_EXT := .pch
 else
-gb_PrecompiledHeader_get_enableflags = -include $(notdir $(subst .gch,,$(call gb_PrecompiledHeader_get_target,$(1),$(2)))) \
-				       -I $(dir $(call gb_PrecompiledHeader_get_target,$(1),$(2)))
+gb_PrecompiledHeader_get_enableflags = \
+-include $(dir $(call gb_PrecompiledHeader_get_target,$(1),$(2)))$(notdir $(subst .gch,,$(call gb_PrecompiledHeader_get_target,$(1),$(2))))
 gb_PrecompiledHeader_EXT := .gch
 endif