bsd.sys.mk: add NO_WCHARACTER_CONVERSION and use it for googletest

This silences warnings about benign implicit character conversions in
googletest's gtest-printers.h.

lib/googletest/Makefile.inc

@@ -10,3 +10,6 @@ CXXFLAGS+=	${GTESTS_FLAGS}
 
 # Silence warnings about usage of deprecated implicit copy constructors
 CXXWARNFLAGS+=  -Wno-deprecated-copy
+
+# Silence warnings about implicit character conversions in gtest-printers.h
+CXXWARNFLAGS+=	${NO_WCHARACTER_CONVERSION}

share/mk/bsd.sys.mk

@@ -133,6 +133,9 @@ NO_WARRAY_PARAMETER=	-Wno-array-parameter
 NO_WSTRICT_PROTOTYPES=	-Wno-strict-prototypes
 NO_WDEPRECATED_NON_PROTOTYPE=-Wno-deprecated-non-prototype
 .endif
+.if ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} >= 210000
+NO_WCHARACTER_CONVERSION=-Wno-character-conversion
+.endif
 .if ${COMPILER_TYPE} == "gcc" && ${COMPILER_VERSION} >= 50200
 NO_WUNUSED_BUT_SET_VARIABLE=-Wno-unused-but-set-variable
 .endif

share/mk/googletest.test.inc.mk

@@ -10,3 +10,6 @@ GTESTS_CXXFLAGS+= -frtti
 CXXFLAGS+=	-I${DESTDIR}${INCLUDEDIR}/private
 
 NO_WTHREAD_SAFETY=
+
+# Silence warnings about implicit character conversions in gtest-printers.h
+CXXWARNFLAGS+=	${NO_WCHARACTER_CONVERSION}