gcc: bump 4.8.x series to version 4.8.3

Update 900-musl-support.patch with upstreamed chunks.

Now upstreamed hence dropped:
840-PR57717.patch (in another way).
842-gcc-4.8.2-Fix-PR-target-58854.patch
843-gcc-4.8.2-Fix-PR-target-58595.patch
850-xtensa-libgcc-linker-script.patch

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>