[CIR][CIRGen] Support __builtin_signbitl (llvm#1117)

follow llvm/clangir#1033
handle `LongDoubleType` with `FP80Type`.

Author: PikachuHyA

clang/test/CIR/CodeGen/builtin-signbit.c

@@ -30,3 +30,13 @@ void test_signbit_long_double(long double val) {
     // LLVM: [[TMP1:%.*]] = bitcast x86_fp80 %{{.+}} to i80
     // LLVM: [[TMP2:%.*]] = icmp slt i80 [[TMP1]], 0
 }
+
+void test_signbit_long_double(long double val) {
+    // CIR: test_signbit_long_double
+    // LLVM: test_signbit_long_double
+    __builtin_signbitl(val);
+    // CIR: %{{.+}} = cir.signbit %{{.+}} : !cir.long_double<!cir.f80> -> !s32i
+    // LLVM: [[TMP1:%.*]] = bitcast x86_fp80 %{{.+}} to i80
+    // LLVM: [[TMP2:%.*]] = icmp slt i80 [[TMP1]], 0
+    // LLVM: %{{.+}} = zext i1 [[TMP2]] to i32
+}