ci: Set ZIG_GLOBAL_CACHE_DIR and ZIG_LOCAL_CACHE_DIR earlier.

Otherwise the disk just keeps getting filled up.

Also remove some pointless cleanup commands since the actions/checkout workflow
step already cleans the repository by default.

ci/aarch64-linux-debug.sh

@@ -19,19 +19,18 @@ export PATH="$HOME/local/bin:$PATH"
 git fetch --unshallow || true
 git fetch --tags
 
-export CC="$ZIG cc -target $TARGET -mcpu=$MCPU"
-export CXX="$ZIG c++ -target $TARGET -mcpu=$MCPU"
-
-rm -rf build-debug
-mkdir build-debug
-cd build-debug
-
 # Override the cache directories because they won't actually help other CI runs
 # which will be testing alternate versions of zig, and ultimately would just
 # fill up space on the hard drive for no reason.
 export ZIG_GLOBAL_CACHE_DIR="$PWD/zig-global-cache"
 export ZIG_LOCAL_CACHE_DIR="$PWD/zig-local-cache"
 
+mkdir build-debug
+cd build-debug
+
+export CC="$ZIG cc -target $TARGET -mcpu=$MCPU"
+export CXX="$ZIG c++ -target $TARGET -mcpu=$MCPU"
+
 cmake .. \
   -DCMAKE_INSTALL_PREFIX="stage3-debug" \
   -DCMAKE_PREFIX_PATH="$PREFIX" \
@@ -66,12 +65,9 @@ stage3-debug/bin/zig build test docs \
 # Ensure that updating the wasm binary from this commit will result in a viable build.
 stage3-debug/bin/zig build update-zig1
 
-rm -rf ../build-new
 mkdir ../build-new
 cd ../build-new
 
-export ZIG_GLOBAL_CACHE_DIR="$PWD/zig-global-cache"
-export ZIG_LOCAL_CACHE_DIR="$PWD/zig-local-cache"
 export CC="$ZIG cc -target $TARGET -mcpu=$MCPU"
 export CXX="$ZIG c++ -target $TARGET -mcpu=$MCPU"