Add toolchain_clang build support

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

llvm.spec

@@ -1,6 +1,11 @@
 %bcond_without sys_llvm
 %bcond_without check
 %bcond_with classic_flang
+%bcond_without toolchain_clang
+
+%if %{with toolchain_clang}
+%global toolchain clang
+%endif
 
 %global maj_ver 17
 %global min_ver 0
@@ -38,7 +43,7 @@
 
 Name:		%{pkg_name}
 Version:	%{maj_ver}.%{min_ver}.%{patch_ver}
-Release:	10
+Release:	11
 Summary:	The Low Level Virtual Machine
 
 License:	NCSA
@@ -85,6 +90,9 @@ BuildRequires:	python3-recommonmark
 BuildRequires:	python3-sphinx
 BuildRequires:	python3-setuptools
 BuildRequires:	zlib-devel
+%if %{with toolchain_clang}
+BuildRequires:	clang
+%endif
 
 Requires:	%{name}-libs%{?_isa} = %{version}-%{release}
 
@@ -230,6 +238,10 @@ cd _build
 %endif
 %if %{with classic_flang}
         -DLLVM_ENABLE_CLASSIC_FLANG=ON \
+%endif
+%if "%{toolchain}" == "clang"
+	-DCMAKE_C_COMPILER=clang \
+	-DCMAKE_CXX_COMPILER=clang++ \
 %endif
 	-DLLVM_INCLUDE_BENCHMARKS=OFF
 %ninja_build LLVM
@@ -353,6 +365,9 @@ LD_LIBRARY_PATH=%{buildroot}/%{install_libdir}  %{__ninja} check-all -C ./_build
 %{install_includedir}/llvm-gmock
 
 %changelog
+* Fri Jul 5 2024 liyunfei <liyunfei33@huawei.com> - 17.0.6-11
+- Add toolchain_clang build support
+
 * Mon Apr 29 2024 wangqiang <wangqiang1@kylinos.cn> - 17.0.6-10
 - Update llvm-lit config to support macro `build_for_openeuler`