Bundle: Tweaks to bootstrap bunlder

It seems running vcvarsall from inside Git bash
does not make proper change in the environment.

Workaround is to have separate script, which
sets environment up and calls bash scripts.

bundle/bundle-linux.sh

@@ -64,20 +64,14 @@ elif [ "${KERNEL_NAME}" == "Darwin" ]; then
   MACHINE_TYPE="x86_64"
   BITNESS="64"
 elif [[ "${KERNEL_NAME}" == "MINGW"* ]]; then
-  if [ -z "${MSVC_ARCH}" ]; then
-    echo "ERROR: On Windows MSVC_ARCH is to be set to either x86 or x64."
-    exit 1
-  fi
-  if [ "${MSVC_ARCH}" == "x64" ]; then
+  if [ "${VSCMD_ARG_TGT_ARCH}" == "x64" ]; then
     BITNESS="64"
-  elif [ "${MSVC_ARCH}" == "x86" ]; then
+  elif [ "${VSCMD_ARG_TGT_ARCH}" == "x86" ]; then
     BITNESS="32"
   else
-    echo "ERROR: Unkown MSVC architecture ${MSVC_ARCH}"
+    echo "Can not detect bitness, running outside of bundle-windows.bat?"
     exit 1
   fi
-  # TODO(sergey): Detect MSVC install somehow.
-  "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvarsall.bat" "${MSVC_ARCH}"
 fi
 
 SVN_BENCHMARK_URL="https://svn.blender.org/svnroot/bf-blender/trunk/lib/benchmarks/cycles/"
@@ -99,6 +93,14 @@ if [ "${KERNEL_NAME}" == "Linux" ]; then
 elif [ "${KERNEL_NAME}" == "Darwin" ]; then
   BLENDER_PLATFORM="macOS-10.6"
   BLENDER_PLATFORM_AND_EXTENSION="${BLENDER_PLATFORM}.zip"
+elif [[ "${KERNEL_NAME}" == "MINGW"* ]]; then
+  if [ "${BITNESS}" == "64" ]; then
+    BLENDER_PLATFORM="windows64"
+    BLENDER_PLATFORM_AND_EXTENSION="${BLENDER_PLATFORM}.tar.bz2"
+  else
+    BLENDER_PLATFORM="windows32"
+    BLENDER_PLATFORM_AND_EXTENSION="${BLENDER_PLATFORM}.tar.bz2"
+  fi
 else
   echo "ERROR: Unsupported platform."
   exit 1