[lib++][CI] Changes bootstrap build type. (#88175)

The RelWithDebInfo generates a few GB of debug info that is not used.
Instead use the normal Release build for testing.

Author: mordante

libcxx/utils/ci/run-buildbot

@@ -374,7 +374,7 @@ bootstrapping-build)
           -B "${BUILD_DIR}" \
           -GNinja -DCMAKE_MAKE_PROGRAM="${NINJA}" \
           -DCMAKE_CXX_COMPILER_LAUNCHER="ccache" \
-          -DCMAKE_BUILD_TYPE=RelWithDebInfo \
+          -DCMAKE_BUILD_TYPE=Release \
           -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}" \
           -DLLVM_ENABLE_PROJECTS="clang" \
           -DLLVM_ENABLE_RUNTIMES="libcxx;libcxxabi;libunwind" \