Add scripts to build SPIR-V plugins

* These are the shader tools we ship with official builds. Most people don't
  need these scripts, but here they are just in case (and so I don't lose them).

util/spirv-plugins/README.md

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+# SPIR-V open source plugins build
+
+These scripts are used to build the latest versions of glslang, SPIRV-Cross and SPIRV-Tools for distribution as plugins. On windows this is just a regular build really, on linux it will build in the renderdoc docker with static linking, to ensure maximum compatibility.
+
+**Most users don't need to build this.**. The pre-built latest plugins packages are provided online which are included in every build, that you can download yourself:
+
+* Windows: https://renderdoc.org/plugins.zip
+* Linux: https://renderdoc.org/plugins.tgz
+
+These scripts are just here so that a RenderDoc developer can update the plugins when needed.

util/spirv-plugins/_build.sh

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+#!/bin/bash
+
+PLATFORM=$1
+OUT=$2
+
+set -ex
+
+# Freshly clone repositories
+rm -rf glslang SPIRV-Cross
+git clone https://github.com/KhronosGroup/glslang
+git clone https://github.com/KhronosGroup/SPIRV-Cross
+
+GENERATOR="Unix Makefiles"
+
+if [ "$PLATFORM" == "win64" ]; then
+	GENERATOR="Visual Studio 15 2017 Win64";
+elif [ "$PLATFORM" == "win32" ]; then
+	GENERATOR="Visual Studio 15 2017";
+else
+	export CC=clang CXX=clang++ CFLAGS="-fPIC -fvisibility=hidden" LDFLAGS="-static-libstdc++"
+fi
+
+##### SPIRV-Cross
+
+pushd SPIRV-Cross
+
+	mkdir build
+	pushd build
+
+		cmake .. -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="${OUT}"
+
+		if [ "${PLATFORM:0:3}" == "win" ]; then
+			cmake --build . --config Release --target install
+		else
+			make -j$(nproc) install
+		fi
+
+	popd #build
+
+popd # SPIRV-Cross
+
+
+##### glslang (and bonus SPIRV-Tools for free)
+pushd glslang
+
+	# Update external sources
+	python update_glslang_sources.py
+
+	# Now build
+	mkdir build
+	pushd build
+
+		# Hack for now until there's a cmake option to turn this off.
+		export CXXFLAGS="-USPIRV_TIMER_ENABLED"
+	
+		cmake .. -DSPIRV_SKIP_TESTS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="${OUT}"
+
+		if [ "${PLATFORM:0:3}" == "win" ]; then
+			cmake --build . --config Release --target install
+		else
+			make -j$(nproc) install
+		fi
+
+	popd #build
+
+popd # glslang
+
+

util/spirv-plugins/build_spirv_plugins.sh

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+#!/bin/bash
+
+if [ ! -f build_spirv_plugins.sh ]; then
+	echo "Run this script from its folder like './build_spirv_plugins.sh'";
+	exit 1;
+fi
+
+if uname -a | grep -qiE 'win|msys|cygwin|microsoft'; then
+	# Windows build
+
+	echo "Building for win32";
+	./_build.sh win32 $(pwd)/spirv-plugins-win32
+
+	echo "Building for win64";
+	./_build.sh win64 $(pwd)/spirv-plugins-win64
+else
+	# Linux build
+
+	if docker image ls | grep -q renderdoc-build; then
+		echo "Building for linux";
+
+		docker run --rm -v $(pwd):/script:ro -v $(pwd)/spirv-plugins-linux64:/out renderdoc-build bash /script/_build.sh linux64 /out
+
+		strip --strip-unneeded spirv-plugins-linux64/bin/*
+	else
+		echo "Run normal RenderDoc build first to generate renderdoc-build image";
+		exit 1;
+	fi
+fi