librsvg: Fix vendored libc to work on riscv and musl

These are patches applied to rust libc already but since librsvg uses
its own copy of libc, we need to patch it here too

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>