Omit musl's stdarg.h and stddef.h from the sysroot.

We already use the compiler's versions of these; this just moves from
having libc #include_next them to having libc just omit them entirely,
which is simpler.

This removes the special code to define musl's include guard, however
I originally added that when I was still working out how WASI's stddef.h
would interact with other code. I believe it's no longer important.

Makefile

@@ -243,6 +243,11 @@ override MUSL_OMIT_HEADERS += \
     "bits/alltypes.h.in" \
     "alltypes.h.in"
 
+# Use the compiler's version of these headers.
+override MUSL_OMIT_HEADERS += \
+    "stdarg.h" \
+    "stddef.h"
+
 # Use the WASI errno definitions.
 override MUSL_OMIT_HEADERS += \
     "bits/errno.h"

expected/wasm32-wasi/include-all.c

@@ -120,10 +120,8 @@
 #include <semaphore.h>
 #include <signal.h>
 #include <stdalign.h>
-#include <stdarg.h>
 #include <stdbool.h>
 #include <stdc-predef.h>
-#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdio_ext.h>

expected/wasm32-wasi/predefined-macros.txt

@@ -2370,7 +2370,6 @@
 #define _STDALIGN_H 
 #define _STDBOOL_H 
 #define _STDC_PREDEF_H 
-#define _STDDEF_H 
 #define _STDINT_H 
 #define _STDIO_EXT_H 
 #define _STDIO_H 

libc-top-half/musl/include/stdarg.h

@@ -1,4 +1,3 @@
-#ifdef __wasilibc_unmodified_upstream /* Use the compiler's stdarg.h */
 #ifndef _STDARG_H
 #define _STDARG_H
 
@@ -20,7 +19,3 @@ extern "C" {
 #endif
 
 #endif
-#else
-/* Just use the compiler's stdarg.h. */
-#include_next <stdarg.h>
-#endif

libc-top-half/musl/include/stddef.h

@@ -1,4 +1,3 @@
-#ifdef __wasilibc_unmodified_upstream /* Use the compiler's stddef.h */
 #ifndef _STDDEF_H
 #define _STDDEF_H
 
@@ -24,14 +23,3 @@
 #endif
 
 #endif
-#else
-
-/* Just use the compiler's stddef.h. */
-#include_next <stddef.h>
-
-/* Define musl's include guard, in case any code depends on that. */
-#if defined(__STDDEF_H) && !defined(_STDDEF_H)
-#define _STDDEF_H
-#endif
-
-#endif