cc.v: build with "implicit-function-declaration" and fix declarations

required for the webassembly backend

2

compiler/cc.v

@@ -39,6 +39,9 @@ fn (v mut V) cc() {
 	else {
 		a << '-g'
 	}
+	if v.os != .msvc {
+		a << '-Werror=implicit-function-declaration'
+	}
 
 	for f in v.generate_hotcode_reloading_compiler_flags() {
 		a << f

compiler/cheaders.v

@@ -11,6 +11,11 @@ CommonCHeaders = '
 #include <inttypes.h>  // int64_t etc
 #include <string.h> // memcpy
 
+#ifndef _WIN32
+#include <ctype.h>
+#include <locale.h> // tolower
+#endif
+
 #define EMPTY_STRUCT_DECLARATION
 #define OPTION_CAST(x) (x)