Add PowerPC64 to CI matrix

Adds just the ppc64le-linux to the CI test matrix with QEMU emulation.

Local testing performed:
- Verified YAML syntax is valid (python yaml.safe_load)
- Confirmed gcc-powerpc64le-linux-gnu packge exists in apt
- Verified qemu-ppc64le can execute PPC64 binaries (exit code test)
- Built origin for powerpc64le-unknown-linux-gnu target successfully

MIPS32 CI is not included because rust-std for mipsel-unknown-linux-gnu
is not available for download (available = false in channel manifest).
Adding MIPS would probably work only through -Zbuild-std, which only
works on nightly, and would add some extra complexity. The MIPS code
is tested by rustfmt and compilation checks but not runtime-tested in CI.

Author: walruscraft

.github/workflows/main.yml

@@ -22,7 +22,7 @@ jobs:
       QEMU_BUILD_VERSION: 8.1.0
     strategy:
       matrix:
-        build: [ubuntu, i686-linux, aarch64-linux, riscv64-linux, mipsel-linux, ppc64le-linux]
+        build: [ubuntu, i686-linux, aarch64-linux, riscv64-linux, ppc64le-linux]
         rust: [1.88, nightly-2025-10-23]
         include:
           - build: ubuntu
@@ -51,14 +51,6 @@ jobs:
             qemu: qemu-riscv64 -L /usr/riscv64-linux-gnu
             qemu_target: riscv64-linux-user
             host_target: riscv64gc-unknown-linux-gnu
-          - build: mipsel-linux
-            os: ubuntu-latest
-            target: mipsel-unknown-linux-gnu
-            gcc_package: gcc-mipsel-linux-gnu
-            gcc: mipsel-linux-gnu-gcc
-            qemu: qemu-mipsel -L /usr/mipsel-linux-gnu
-            qemu_target: mipsel-linux-user
-            host_target: mipsel-unknown-linux-gnu
           - build: ppc64le-linux
             os: ubuntu-latest
             target: powerpc64le-unknown-linux-gnu