wchar.h: fix header comment style.

Comment uses C++ style, while it can be compiled in a C-only environment. This
broke the ICU cross compilation (done for ARM).

headers/posix/wchar.h

@@ -30,7 +30,7 @@ typedef struct {
 	void* converter;
 	char charset[64];
 	unsigned int count;
-	char data[1024 + 8];	// 1024 bytes for data, 8 for alignment space
+	char data[1024 + 8];	/* 1024 bytes for data, 8 for alignment space */
 } mbstate_t;