Rework the CI to build inside the valve sniper sdk container thing (#56)

.github/workflows/build.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+set -euxo pipefail
+
+cd "$(dirname $0)/../.."
+
+if [[ $PLATFORM == Linux* ]]; then
+	$CC --version
+	$CXX --version
+
+	apt install -y python3-pip
+
+	# buildbot/generate_header.py is ran by ambuild and we want git to not fail due to user-perms (because docker)
+	git config --global --add safe.directory $PWD
+else
+	python -m pip install --upgrade pip setuptools wheel
+fi
+
+python -m pip install $CACHE_PATH/ambuild
+
+mkdir build
+cd build
+python ../configure.py --enable-auto-versioning --enable-optimize --sdks="$SDKS" --mms-path="$CACHE_PATH/metamod-source" --hl2sdk-root="$CACHE_PATH" --sm-path="$CACHE_PATH/sourcemod"
+ambuild