[CodeGen] remove creation of FP cast function attribute

[spatel]

Summary

This is the last cleanup step resulting from D115804 .
Now that clang uses intrinsics when we're in the special FP mode, we don't need a function attribute as an indicator to the backend. The LLVM part of the change is in D115885.

[pengfei]

LGTM.

clang/lib/CodeGen/CGCall.cpp

if (CodeGenOpts.FP32DenormalMode != CodeGenOpts.FPDenormalMode) {
       FuncAttrs.addAttribute(
           "denormal-fp-math-f32",
           CodeGenOpts.FP32DenormalMode.str());
     }
 
     if (LangOpts.getFPExceptionMode() == LangOptions::FPE_Ignore)
       FuncAttrs.addAttribute("no-trapping-math", "true");
 
-    // Strict (compliant) code is the default, so only add this attribute to
-    // indicate that we are trying to workaround a problem case.
-    if (!CodeGenOpts.StrictFloatCastOverflow)
-      FuncAttrs.addAttribute("strict-float-cast-overflow", "false");
-
     // TODO: Are these all needed?
     // unsafe/inf/nan/nsz are handled by instruction-level FastMathFlags.
     if (LangOpts.NoHonorInfs)
       FuncAttrs.addAttribute("no-infs-fp-math", "true");
     if (LangOpts.NoHonorNaNs)
       FuncAttrs.addAttribute("no-nans-fp-math", "true");
     if (LangOpts.ApproxFunc)
       FuncAttrs.addAttribute("approx-func-fp-math", "true");

clang/test/CodeGen/no-junk-ftrunc.c

 // RUN: %clang_cc1 -S -fno-strict-float-cast-overflow %s -emit-llvm -o - | FileCheck %s --check-prefix=NOSTRICT
 
 // When compiling with non-standard semantics, use intrinsics to inhibit the optimizer.
+// This used to require a function attribute, so we check that it is NOT here anymore.
 
 // NOSTRICT-LABEL: main
 // NOSTRICT: call i32 @llvm.fptosi.sat.i32.f64
 // NOSTRICT: call i32 @llvm.fptoui.sat.i32.f64
-// NOSTRICT: attributes #0 = {{.*}}"strict-float-cast-overflow"="false"{{.*}}
+// NOSTRICT-NOT: strict-float-cast-overflow
 
 // The workaround attribute is not applied by default.
 
 // RUN: %clang_cc1 -S %s -emit-llvm -o - | FileCheck %s --check-prefix=STRICT
 // STRICT-LABEL: main
 // STRICT: = fptosi
 // STRICT: = fptoui
 // STRICT-NOT: strict-float-cast-overflow
 
 
 int main() {
   double d = 1e20;
   return (int)d != 1e20 && (unsigned)d != 1e20;
 }