[WebAssembly] Add options for using the nontrapping-fptoint feature.

This adds ways to control use of WebAssembly's new nontrapping-fptoint
feature.

llvm-svn: 319129
diff --git a/clang/lib/Basic/Targets/WebAssembly.cpp b/clang/lib/Basic/Targets/WebAssembly.cpp
index 9eaaf8d..915aad4 100644
--- a/clang/lib/Basic/Targets/WebAssembly.cpp
+++ b/clang/lib/Basic/Targets/WebAssembly.cpp
@@ -32,6 +32,7 @@
 bool WebAssemblyTargetInfo::hasFeature(StringRef Feature) const {
   return llvm::StringSwitch<bool>(Feature)
       .Case("simd128", SIMDLevel >= SIMD128)
+      .Case("nontrapping-fptoint", HasNontrappingFPToInt)
       .Default(false);
 }
 
@@ -61,6 +62,14 @@
       SIMDLevel = std::min(SIMDLevel, SIMDEnum(SIMD128 - 1));
       continue;
     }
+    if (Feature == "+nontrapping-fptoint") {
+      HasNontrappingFPToInt = true;
+      continue;
+    }
+    if (Feature == "-nontrapping-fptoint") {
+      HasNontrappingFPToInt = false;
+      continue;
+    }
 
     Diags.Report(diag::err_opt_not_valid_with_opt)
         << Feature << "-target-feature";