Bump std= to c11 since we use _Atomic (a C11 addition) in threadwrap

src/build/Common.gmake

@@ -480,7 +480,7 @@ $(OBJODIR)/%$(OFILE) : %.s $(BUILD_DEPENDS) | $(OBJODIR)
 # Implicit C Compile Rule
 $(OBJODIR)/%$(OFILE) : %.c $(BUILD_DEPENDS) | $(OBJODIR)
 	@echo $(COMPILE_MSG) $<
-	$(QUIET)$(CC) -std=c99 $(CFLAGS) $(CCFLAGS) -o $@ -c $<
+	$(QUIET)$(CC) -std=c11 $(CFLAGS) $(CCFLAGS) -o $@ -c $<
 
 # Implicit C++ Compile Rule
 $(OBJODIR)/%$(OFILE) : %.cpp $(BUILD_DEPENDS) | $(OBJODIR)
@@ -495,7 +495,7 @@ $(MTOBJODIR)/%$(OFILE) : %.s $(BUILD_DEPENDS) | $(OBJODIR)
 # Implicit MT C Compile Rule
 $(MTOBJODIR)/%$(OFILE) : %.c $(BUILD_DEPENDS) | $(MTOBJODIR)
 	@echo $(COMPILE_MSG) $<
-	$(QUIET)$(CC) -std=c99 $(CFLAGS) $(CCFLAGS) $(MT_CFLAGS) -o $@ -c $<
+	$(QUIET)$(CC) -std=c11 $(CFLAGS) $(CCFLAGS) $(MT_CFLAGS) -o $@ -c $<
 
 # Implicit MT C++ Compile Rule
 $(MTOBJODIR)/%$(OFILE) : %.cpp $(BUILD_DEPENDS) | $(MTOBJODIR)