Add toolchain_clang build support

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

clang.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
@@ -37,7 +42,7 @@
 
 Name:		%{pkg_name}
 Version:	%{clang_version}
-Release:	17
+Release:	18
 Summary:	A C language family front-end for LLVM
 
 License:	NCSA
@@ -108,6 +113,9 @@ BuildRequires: perl(lib)
 BuildRequires: perl(Term::ANSIColor)
 BuildRequires: perl(Text::ParseWords)
 BuildRequires: perl(Sys::Hostname)
+%if %{with toolchain_clang}
+BuildRequires:	clang
+%endif
 
 Requires:	%{name}-libs%{?_isa} = %{version}-%{release}
 
@@ -269,6 +277,10 @@ cd _build
         -DLLVM_ENABLE_CLASSIC_FLANG=ON \
 %endif
 	-DBUILD_FOR_OPENEULER=ON \
+%if "%{toolchain}" == "clang"
+	-DCMAKE_C_COMPILER=clang \
+	-DCMAKE_CXX_COMPILER=clang++ \
+%endif
 	-DCLANG_DEFAULT_UNWINDLIB=libgcc
 
 %ninja_build
@@ -395,6 +407,9 @@ LD_LIBRARY_PATH=%{buildroot}/%{install_libdir}  %{__ninja} check-all -C ./_build
 %{install_bindir}/git-clang-format
 
 %changelog
+* Fri Jul 5 2024 liyunfei <liyunfei33@huawei.com> - 17.0.6-18
+- Add toolchain_clang build support
+
 * Tue Jun 04 2024 Zhao Mengmeng <zhaomengmeng@kylinos.cn> - 17.0.6-17
 - Fix the too-early instantiation of conditional "explict" by applying the patch
   of https://github.com/llvm/llvm-project/commit/128b3b61fe6768c724975fd1df2be0abec848cf6