Optimize vlc_memstream_puts() with constant string

If the string given to vlc_memstream_puts() is constant, or at least
its length is constant, use vlc_memstream_write() instead and let GCC
compute the length at build-time.

include/vlc_memstream.h

@@ -62,4 +62,15 @@ VLC_API
 int vlc_memstream_printf(struct vlc_memstream *s, const char *fmt,
                          ...) VLC_FORMAT(2,3);
 
+# ifdef __GNUC__
+static inline int vlc_memstream_puts_len(struct vlc_memstream *ms,
+                                         const char *str, size_t len)
+{
+    return (vlc_memstream_write(ms, str, len) == len) ? (int)len : EOF;
+}
+#  define vlc_memstream_puts(ms,s) \
+    (__builtin_constant_p(__builtin_strlen(s)) ? \
+        vlc_memstream_puts_len(ms,s,__builtin_strlen(s)) : \
+        vlc_memstream_puts(ms,s))
+# endif
 #endif /* VLC_MEMSTREAM_H */

src/text/memstream.c

@@ -82,7 +82,7 @@ int vlc_memstream_putc(struct vlc_memstream *ms, int c)
     return fputc(c, ms->stream);
 }
 
-int vlc_memstream_puts(struct vlc_memstream *ms, const char *str)
+int (vlc_memstream_puts)(struct vlc_memstream *ms, const char *str)
 {
     if (unlikely(ms->stream == NULL))
         return EOF;
@@ -145,7 +145,7 @@ int vlc_memstream_putc(struct vlc_memstream *ms, int c)
     return (vlc_memstream_write(ms, &(unsigned char){ c }, 1u) == 1) ? c : EOF;
 }
 
-int vlc_memstream_puts(struct vlc_memstream *ms, const char *str)
+int (vlc_memstream_puts)(struct vlc_memstream *ms, const char *str)
 {
     size_t len = strlen(str);
     return (vlc_memstream_write(ms, str, len) == len) ? 0 : EOF;