[clang][RISCV][test] Add coverage for __fp16 support in arguments/ret…

…urns

By choice, we don't set HalfArgsAndReturns=true (which would allow
__fp16 in args and returns). Add test coverage for this to ensure it
isn't changed by accident.

clang/test/Sema/riscv-fp16.c

@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -fsyntax-only -triple riscv32 -Wno-strict-prototypes -verify %s
+// RUN: %clang_cc1 -fsyntax-only -triple riscv64 -Wno-strict-prototypes -verify %s
+// REQUIRES: riscv-registered-target
+
+// Functions cannot have parameters of type __fp16.
+extern void f (__fp16); // expected-error {{parameters cannot have __fp16 type; did you forget * ?}}
+extern void g (__fp16 *);
+
+extern void (*pf) (__fp16);  // expected-error {{parameters cannot have __fp16 type; did you forget * ?}}
+extern void (*pg) (__fp16*);
+
+typedef void(*tf) (__fp16);  // expected-error {{parameters cannot have __fp16 type; did you forget * ?}}
+typedef void(*tg) (__fp16*);
+
+void kf(a)
+ __fp16 a; {  // expected-error {{parameters cannot have __fp16 type; did you forget * ?}}
+}
+
+void kg(a)
+ __fp16 *a; {
+}
+
+// Functions cannot return type __fp16.
+extern __fp16 f1 (void); // expected-error {{function return value cannot have __fp16 type; did you forget * ?}}
+extern __fp16 *g1 (void);
+
+extern __fp16 (*pf1) (void); // expected-error {{function return value cannot have __fp16 type; did you forget * ?}}
+extern __fp16 *(*gf1) (void);
+
+typedef __fp16 (*tf1) (void); // expected-error {{function return value cannot have __fp16 type; did you forget * ?}}
+typedef __fp16 *(*tg1) (void);
+
+void testComplex() {
+  // FIXME: Should these be valid?
+  _Complex __fp16 a; // expected-error {{'_Complex half' is invalid}}
+  __fp16 b;
+  a = __builtin_complex(b, b); // expected-error {{'_Complex half' is invalid}}
+}