wasm32-unknown-unknown: Fix undefined malloc/free/calloc symbols (#275)

As discussed in #250, in some
cases the definitions of `malloc`, `free`, and `calloc` are used but
don't get linked in, leading to undefined symbols (i.e. reference to the
symbol in "env").

I was not able to determine exactly why this is happening, but it seems
to be related to `malloc`, `calloc`, and `free` being defined as inline
functions.  When building in debug mode there are undefined symbols;
when building in release mode there are not, presumably because the
functions are inlined.

Switching to macros avoids issues of inlining and fixes this issue for
me.

zstd-safe/zstd-sys/wasm-shim/stdlib.h

@@ -1,28 +1,18 @@
 #include <stddef.h>
 
-#ifndef	_STDLIB_H
-#define	_STDLIB_H	1
+#ifndef _STDLIB_H
+#define _STDLIB_H 1
 
-void *rust_zstd_wasm_shim_malloc(size_t size);
-void *rust_zstd_wasm_shim_calloc(size_t nmemb, size_t size);
-void rust_zstd_wasm_shim_free(void *ptr);
-void rust_zstd_wasm_shim_qsort(void *base, size_t nitems, size_t size, int (*compar)(const void *, const void*));
+void* rust_zstd_wasm_shim_malloc(size_t size);
+void* rust_zstd_wasm_shim_calloc(size_t nmemb, size_t size);
+void rust_zstd_wasm_shim_free(void* ptr);
+void rust_zstd_wasm_shim_qsort(void* base, size_t nitems, size_t size,
+                               int (*compar)(const void*, const void*));
 
-inline void *malloc(size_t size) {
-	return rust_zstd_wasm_shim_malloc(size);
-}
+#define malloc(size) rust_zstd_wasm_shim_malloc(size)
+#define calloc(nmemb, size) rust_zstd_wasm_shim_calloc(nmemb, size)
+#define free(ptr) rust_zstd_wasm_shim_free(ptr)
+#define qsort(base, nitems, size, compar) \
+  rust_zstd_wasm_shim_qsort(base, nitems, size, compar)
 
-inline void *calloc(size_t nmemb, size_t size) {
-	return rust_zstd_wasm_shim_calloc(nmemb, size);
-}
-
-inline void free(void *ptr) {
-	rust_zstd_wasm_shim_free(ptr);
-}
-
-inline void qsort(void *base, size_t nitems, size_t size, int (*compar)(const void *, const void*))
-{
-    return rust_zstd_wasm_shim_qsort(base, nitems, size, compar);
-}
-
-#endif // _STDLIB_H
+#endif  // _STDLIB_H