Rename bazel-zig-cc to hermetic_cc_toolchain (#36)

As it says on the tin.

Long live hermetic_cc_toolchain!

ci/launcher

@@ -23,5 +23,5 @@ echo "--- zig fmt --check toolchain/launcher.zig"
 $ZIG fmt --check toolchain/launcher.zig
 
 echo "--- zig test toolchain/launcher.zig"
-# until bazel-zig-cc gets a zig toolchain, run launcher's unit tests here.
+# until hermetic_cc_toolchain gets a zig toolchain, run launcher's unit tests here.
 $ZIG test toolchain/launcher.zig

ci/release

@@ -12,4 +12,4 @@ tools/bazel run //tools/releaser -- -tag v99.0.0
 cleanup() { git tag -d v99.0.0; git reset --hard "$prev_ref"; }
 trap cleanup EXIT
 
-file bazel-zig-cc-v99.0.0.tar.gz | grep -q 'gzip compressed data'
+file hermetic_cc_toolchain-v99.0.0.tar.gz | grep -q 'gzip compressed data'

ci/test

@@ -5,7 +5,7 @@
 
 set -xeuo pipefail
 
-cache_prefix="${BAZEL_ZIG_CC_CACHE_PREFIX:-/tmp/bazel-zig-cc}"
+cache_prefix="${HERMETIC_CC_TOOLCHAIN_CACHE_PREFIX:-/tmp/hermetic_cc_toolchain}"
 
 # check a very hermetic setup with a single target. Re-building all of
 # them takes a long time, so using only one. If we ever decide to build all