wasm: support more vendor libraries

Adds support for:
- box2d
- cgltf
- stb image
- stb rect pack

vendor/libc/include/stdlib.h

@@ -0,0 +1,19 @@
+#include <stddef.h>
+
+void *malloc(size_t size);
+
+void *aligned_alloc(size_t alignment, size_t size);
+
+void free(void *);
+
+void *realloc(void *, size_t);
+
+void qsort(void* base, size_t num, size_t size, int (*compare)(const void*, const void*));
+
+int atoi(const char *);
+long atol(const char *);
+long long atoll(const char *);
+
+double atof(const char *);
+
+long strtol(const char *, char **, int);