Add -MG

This option allows for automatic dependency detection and generation:
as soon as a missing file is found, it is output to the dep file, and
assembly immediately aborts. (No .o file is produced, even if `-o` was
speicified.) This doesn't cause an error, either; the point is that once
the file is added to the dep file, the Makefile is re-parsed, and this
time the file will be generated, so the dep list builds up automatically.
This mimicks GCC's option and behavior.

include/asm/main.h

@@ -36,7 +36,8 @@ extern struct sOptions CurrentOptions;
 
 extern FILE *dependfile;
 extern char *tzTargetFileName;
-
+extern bool oGeneratedMissingIncludes;
+extern bool oFailedOnMissingInclude;
 extern bool oGeneratePhonyDeps;
 
 void opt_Push(void);