Use BUILD_TYPE in cmake_build.

Build files were directly written to the out directory. This change makes them go to the expected out/{Release, Debug} directory.

BUG=skia:5160

GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1916773002
CQ_EXTRA_TRYBOTS=client.skia.compile:Build-Ubuntu-GCC-x86_64-Release-CMake-Trybot,Build-Mac-Clang-x86_64-Release-CMake-Trybot

Review URL: https://codereview.chromium.org/1916773002
diff --git a/cmake/cmake_build b/cmake/cmake_build
index 861453e..f2cb9bf 100755
--- a/cmake/cmake_build
+++ b/cmake/cmake_build
@@ -26,8 +26,8 @@
 popd
 
 echo "Building with bootstrapped CMake"
-mkdir -p $SKIA_OUT
-pushd $SKIA_OUT
+mkdir -p $SKIA_OUT/$BUILDTYPE
+pushd $SKIA_OUT/$BUILDTYPE
 $here/../third_party/externals/cmake/bin/cmake -DCMAKE_BUILD_TYPE=$BUILDTYPE $here -G Ninja
 ninja
 popd