Add ccache support for faster incremental builds (#301)

## Description of change
Adds `ccache` support for local compiling and Github Actions
environments. This significantly speeds up incremental builds, but cold
starts will take a little longer to compile.

The build script now has an `-i` flag to ignore the build cache if
needed. You can also manually delete the `.ccache` folder to force a
fresh build too.

For the GA workflow, it uses the
[`ccache-action`](https://github.com/hendrikmuhs/ccache-action) action
to manage and store the cached build objects. This cache should be
accessible to all branches.

I also removed the `--no-cache` flag when building the
`spicetools/spice` image since Docker will automatically invalidate
`COPY` layers if it detects the copied files have changed.

### Compile times
Compiled with a 7800X3D, 32GB 6000MT/s RAM.
| `main` | `ccache` (fresh) | `ccache` (cached) | `ccache` (ignore
cache) |
|--------|--------|--------|--------|
| 2m46.047s | 3m8.886s | 0m32.638s | 2m45.148s |

## Testing
Tested incremental builds by using another branch that's rebased on top
of this.

src/spice2x/build_all.sh

@@ -19,6 +19,25 @@ function trap_error_exit {
 trap trap_error_dbg DEBUG
 trap trap_error_exit EXIT
 
+IGNORE_CACHE=0
+
+# Parse options
+while getopts "ih" opt; do
+  case $opt in
+    i) IGNORE_CACHE=1 ;;
+    h)
+      echo "Usage: $0 [-i]"
+      echo "  -i: Ignore build cache"
+      echo "  -h: Show this help"
+      exit 0
+      ;;
+    \?)
+      echo "Invalid option: -$OPTARG" >&2
+      exit 1
+      ;;
+  esac
+done
+
 # settings
 GIT_BRANCH=$(git rev-parse --abbrev-ref HEAD 2> /dev/null || echo "none")
 GIT_HEAD=$(git rev-parse HEAD || echo "none")
@@ -74,6 +93,15 @@ echo "Build Type: $BUILD_TYPE"
 echo "Cores: $CORES"
 echo ""
 
+if ((IGNORE_CACHE > 0))
+then
+  echo "Ignoring build cache..."
+else
+ export CCACHE_DIR="$(pwd)/.ccache"
+ export CMAKE_CXX_COMPILER_LAUNCHER=ccache
+ export CMAKE_C_COMPILER_LAUNCHER=ccache
+fi
+
 time (
 	# 32 bit
 	echo "Building 32bit targets..."