Clean up more code

- Found some bugs in LLVM compiler-rt library
- The useless LIBC_STUBS package is now deleted
- Improve the overflow checking story even further
- Get chibicc tests working in MODE=dbg mode again
- The libc/isystem/ headers now have correctly named guards

third_party/zip/tailor.h

@@ -224,7 +224,6 @@
 #include "libc/stdio/dprintf.h"
 #include "libc/calls/weirdtypes.h"
 #include "libc/fmt/fmt.h"
-#include "libc/mem/fmt.h"
 #include "libc/stdio/stdio.h"
 #include "libc/stdio/temp.h"
 #include "third_party/musl/tempnam.h"

third_party/zip/zip.c

@@ -88,7 +88,6 @@
 #include "libc/stdio/dprintf.h"
 #include "libc/calls/weirdtypes.h"
 #include "libc/fmt/fmt.h"
-#include "libc/mem/fmt.h"
 #include "libc/stdio/stdio.h"
 #include "libc/stdio/temp.h"
 #include "third_party/musl/tempnam.h"

third_party/zip/zip.mk

@@ -88,7 +88,6 @@ THIRD_PARTY_ZIP_DIRECTDEPS =			\
 	LIBC_RUNTIME				\
 	LIBC_STDIO				\
 	LIBC_STR				\
-	LIBC_STUBS				\
 	LIBC_SYSV				\
 	LIBC_TIME				\
 	LIBC_X					\