Auto merge of rust-lang#117672 - lqd:ci-gcc-lld, r=<try>

ci: bump gcc on dist x64 linux builder to 9.5

Support for `-fuse-ld=lld` was added in GCC 9, so this PR bumps gcc to the latest 9.x release, to prepare for switching to LLD.

`-Clinker-flavor=gnu-lld-cc -Clink-self-contained=+linker` will require our CI's GCC to understand `-fuse-ld=lld` when bootstrapping in a future where `x86_64-unknown-linux-gnu` is using `rust-lld` by default.

r? `@ghost`

src/ci/docker/host-x86_64/dist-x86_64-linux/build-gcc.sh

@@ -3,7 +3,7 @@ set -ex
 
 source shared.sh
 
-GCC=8.5.0
+GCC=9.5.0
 
 curl https://ftp.gnu.org/gnu/gcc/gcc-$GCC/gcc-$GCC.tar.xz | xzcat | tar xf -
 cd gcc-$GCC