Use "__inline" instead of "inline" with MSVC

MSVC supports "inline" only in C++ code, not in C code.

src/config_file.c

@@ -565,7 +565,7 @@ void cfg_consume_line(file_backend *cfg)
 	cfg->reader.read_ptr = line_end;
 }
 
-static inline int config_keychar(int c)
+GIT_INLINE(int) config_keychar(int c)
 {
 	return isalnum(c) || c == '-';
 }