Prevent Clang UB 'optimization' which breaks integerness checks.

Thanks to Kacper Michajłow. #1351 #1355

src/Makefile

@@ -302,6 +302,9 @@ endif
 ifneq (,$(INSTALL_LJLIBD))
   TARGET_XCFLAGS+= -DLUA_LJDIR=\"$(INSTALL_LJLIBD)\"
 endif
+ifeq (,$(shell $(TARGET_CC) -o /dev/null -c -x c /dev/null -fno-strict-float-cast-overflow 2>/dev/null || echo 1))
+  TARGET_XCFLAGS+= -fno-strict-float-cast-overflow
+endif
 
 ##############################################################################
 # Target system detection.