qb: Fix the qt configure check with older compilers.

Makefile

@@ -109,7 +109,7 @@ endif
 DEF_FLAGS += -Wall $(INCLUDE_DIRS) -I. -Ideps -Ideps/stb
 
 CFLAGS += $(DEF_FLAGS)
-CXXFLAGS += $(DEF_FLAGS) -std=c++11 -D__STDC_CONSTANT_MACROS
+CXXFLAGS += $(DEF_FLAGS) -D__STDC_CONSTANT_MACROS
 OBJCFLAGS :=  $(CFLAGS) -D__STDC_CONSTANT_MACROS
 
 ifeq ($(HAVE_CXX), 1)

Makefile.common

@@ -7,6 +7,10 @@ ifeq ($(HAVE_STACK_USAGE), 1)
    DEF_FLAGS += -fstack-usage
 endif
 
+ifeq ($(HAVE_CXX11), 1)
+   CXXFLAGS += $(CXX11_CFLAGS)
+endif
+
 ifeq ($(HAVE_GL_CONTEXT),)
    HAVE_GL_CONTEXT = 0
    HAVE_GL_MODERN  = 0

qb/config.libs.sh

@@ -5,9 +5,10 @@
 # check_header, check_macro and check_switch are not used.
 
 check_switch '' C99 -std=gnu99 "Cannot find C99 compatible compiler."
-check_switch '' NOUNUSED -Wno-unused-result
+check_switch cxx CXX11 -std=c++11 ''
+check_switch '' NOUNUSED -Wno-unused-result ''
 add_define MAKEFILE NOUNUSED "$HAVE_NOUNUSED"
-check_switch '' NOUNUSED_VARIABLE -Wno-unused-variable
+check_switch '' NOUNUSED_VARIABLE -Wno-unused-variable ''
 add_define MAKEFILE NOUNUSED_VARIABLE "$HAVE_NOUNUSED_VARIABLE"
 
 # There are still broken 64-bit Linux distros out there. :)
@@ -264,6 +265,8 @@ if [ "$HAVE_SDL2" = 'yes' ] && [ "$HAVE_SDL" = 'yes' ]; then
    HAVE_SDL=no
 fi
 
+check_enabled CXX11 CXX C++ 'C++11 support is' false
+
 check_platform Haiku DISCORD 'Discord is' false
 check_enabled CXX DISCORD discord 'The C++ compiler is' false
 check_enabled CXX QT 'Qt companion' 'The C++ compiler is' false

qb/config.moc.sh

@@ -1,4 +1,4 @@
 QT_VERSION=qt5
-QT_FLAGS="$QT5CORE_CFLAGS $QT5CORE_LIBS"
+QT_FLAGS="$CXX11_CFLAGS $QT5CORE_CFLAGS $QT5CORE_LIBS"
 
 add_define MAKEFILE QT_VERSION "$QT_VERSION"

qb/qb.libs.sh

@@ -343,12 +343,16 @@ check_switch()
 	printf %s\\n 'int main(void) { return 0; }' > "$TEMP_CODE"
 	answer='no'
 	printf %s "Checking for availability of switch $3 in $COMPILER ... "
-	$(printf %s "$COMPILER") -o "$TEMP_EXE" "$TEMP_CODE" "$3" \
+	$(printf %s "$COMPILER") -o "$TEMP_EXE" "$TEMP_CODE" \
+		$(printf %s "$BUILD_DIRS $CFLAGS $3 -Werror $LDFLAGS") \
 		>>config.log 2>&1 && answer='yes'
 	eval "HAVE_$2=\"$answer\""
 	printf %s\\n "$answer"
 	rm -f -- "$TEMP_CODE" "$TEMP_EXE"
-	if [ "$answer" = 'no' ] && [ "${4:-}" ]; then
+	if [ "$answer" = 'yes' ]; then
+		eval "${2}_CFLAGS=\"$3\""
+		PKG_CONF_USED="$PKG_CONF_USED $2"
+	elif [ "${4:-}" ]; then
 		die 1 "$4"
 	fi
 }