Add toolchain_clang build support

Signed-off-by: liyunfei <liyunfei33@huawei.com>

libcxx.spec

@@ -1,5 +1,10 @@
 %bcond_without sys_llvm
 %bcond_without check
+%bcond_without toolchain_clang
+
+%if %{with toolchain_clang}
+%global toolchain clang
+%endif
 
 %global maj_ver 17
 %global min_ver 0
@@ -33,7 +38,7 @@
 
 Name:       %{pkg_name}
 Version:    %{libcxx_version}
-Release:    1%{?dist}
+Release:    2%{?dist}
 Summary:    LLVM "libcxx" runtime libraries
 License:    Apache-2.0
 URL:        http://llvm.org
@@ -176,6 +181,10 @@ export ASMFLAGS=$CFLA
     -DLIBUNWIND_INCLUDE_DOCS=ON \
     -DLIBUNWIND_INSTALL_INCLUDE_DIR=%{install_includedir}/llvm-libunwind \
     -DLIBUNWIND_INSTALL_SPHINX_HTML_DIR=%{_pkgdocdir}/html \
+%if "%{toolchain}" == "clang"
+	-DCMAKE_C_COMPILER=clang \
+	-DCMAKE_CXX_COMPILER=clang++ \
+%endif
     ..
 
 %ninja_build
@@ -256,6 +265,9 @@ rm %{buildroot}%{_pkgdocdir}/html/.buildinfo
 %doc %{_pkgdocdir}/html
 
 %changelog
+* Fri Jul 5 2024 liyunfei <liyunfei33@huawei.com> - 17.0.6-2
+- Add toolchain_clang build support
+
 * Tue Dec 5 2023 zhoujing <zhoujing106@huawei.com> - 17.0.6-1
 - update to 17.0.6