external/liborcus: Silence clang-cl errors about redeclared Windows functions

...like CreateMutexA redeclared in
workdir/UnpackedTarball/boost\boost/thread/win32/thread_primitives.hpp.  As such
problematic Boost include files are apparently not included from LO-proper
source files, only from external, it looks easiest to just silence that with
BOOST_USE_WINDOWS_H here.

Change-Id: Ia5ec2325934e6d7fdcf91e6faa2e671aee2091ae

external/liborcus/Library_orcus-parser.mk

@@ -29,6 +29,13 @@ $(eval $(call gb_Library_add_defs,orcus-parser,\
 	-DBOOST_ALL_NO_LIB \
 	-D__ORCUS_PSR_BUILDING_DLL \
 ))
+ifeq ($(OS),WNT)
+ifeq ($(COM_IS_CLANG),TRUE)
+$(eval $(call gb_Library_add_defs,orcus-parser, \
+    -DBOOST_USE_WINDOWS_H \
+))
+endif
+endif
 
 $(eval $(call gb_Library_set_generated_cxx_suffix,orcus-parser,cpp))