util: Convert util/u_printf.cpp to util/u_printf.c

By doing this to remove the need of C++ runtime when not using llvmpipe

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Reviewed-by: Mihai Preda <mhpreda@gmail.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15659>

src/util/u_printf.h

@@ -26,12 +26,6 @@
 #include <stddef.h>
 
 #ifdef __cplusplus
-
-#include <string>
-
-/* find next valid printf specifier in a C++ std::string */
-size_t util_printf_next_spec_pos(const std::string &s, size_t pos);
-
 extern "C" {
 #endif