LibC: Make libc usable with tcc

tcc does not provide its own stdint.h but defines everything in
stddef.h. Also tcc does not support [[noreturn]] attribute syntax.

userspace/libraries/LibC/include/assert.h

@@ -13,7 +13,8 @@
 
 __BEGIN_DECLS
 
-[[noreturn]] void __assert_fail(const char*, const char*, int, const char*);
+__attribute__((noreturn))
+void __assert_fail(const char*, const char*, int, const char*);
 
 __END_DECLS
 

userspace/libraries/LibC/include/stdint.h

@@ -0,0 +1,5 @@
+#ifdef __TINYC__
+#include <stddef.h>
+#else
+#include_next <stdint.h>
+#endif