Add testcase

Author: BeMg

clang/test/Sema/attr-target-riscv.c

@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -triple riscv64-linux-gnu -target-feature +i -fsyntax-only -verify -std=c2x %s
+
+//expected-note@+1 {{previous definition is here}}
+int __attribute__((target("arch=rv64g"))) foo(void) { return 0; }
+//expected-error@+1 {{redefinition of 'foo'}}
+int __attribute__((target("arch=rv64gc"))) foo(void) { return 0; }