!80 support clang build when %toolchain == clang

From: @mdLUbG 
Reviewed-by: @Jingwiw, @peijiankang 
Signed-off-by: @Jingwiw, @peijiankang

qt5-qtbase.spec

@@ -16,6 +16,10 @@
 
 %global platform linux-g++
 
+%if "%toolchain" == "clang"
+%global use_clang 1
+%endif
+
 %if 0%{?use_clang}
 %global platform linux-clang
 %endif
@@ -32,7 +36,7 @@
 Name:             qt5-qtbase
 Summary:          Qt5 - QtBase components
 Version:          5.15.10
-Release:          2
+Release:          3
 
 # See LGPL_EXCEPTIONS.txt, for exception details
 License:          LGPL-3.0-only OR GPL-3.0-only WITH Qt-GPL-exception-1.0
@@ -1051,6 +1055,9 @@ fi
 
 
 %changelog
+* Wed Sep 13 2023 yoo <sunyuechi@iscas.ac.cn> - 5.15.10-3
+- support clang build when %toolchain == clang
+
 * Fri Sep 01 2023 wangkai <13474090681@163.com> - 5.15.10-2
 - Fix CVE-2023-37369