all: add target-features string to all targets

This makes sure that the LLVM target features match the one generated by
Clang:

  - This fixes a bug introduced when setting the target CPU for all
    targets: Cortex-M4 would now start using floating point operations
    while they were disabled in C.
  - This will make it possible in the future to inline C functions in Go
    and vice versa. This will need some more work though.

There is a code size impact. Cortex-M4 targets are increased slightly in
binary size while Cortex-M0 targets tend to be reduced a little bit.
Other than that, there is little impact.

builder/build.go

@@ -136,7 +136,6 @@ func Build(pkgName, outpath string, config *compileopts.Config, action func(Buil
 		DefaultStackSize:   config.Target.DefaultStackSize,
 		NeedsStackObjects:  config.NeedsStackObjects(),
 		Debug:              true,
-		LLVMFeatures:       config.LLVMFeatures(),
 	}
 
 	// Load the target machine, which is the LLVM object that contains all

builder/builder_test.go

@@ -12,8 +12,8 @@ import (
 	"tinygo.org/x/go-llvm"
 )
 
-// Test whether the Clang generated "target-cpu" attribute matches the CPU
-// property in TinyGo target files.
+// Test whether the Clang generated "target-cpu" and "target-features"
+// attributes match the CPU and Features property in TinyGo target files.
 func TestClangAttributes(t *testing.T) {
 	var targetNames = []string{
 		// Please keep this list sorted!
@@ -112,16 +112,30 @@ func testClangAttributes(t *testing.T, options *compileopts.Options) {
 		t.Errorf("target has LLVM triple %#v but Clang makes it LLVM triple %#v", config.Triple(), mod.Target())
 	}
 
-	// Check the "target-cpu"  string attribute of the add function.
+	// Check the "target-cpu" and "target-features" string attribute of the add
+	// function.
 	add := mod.NamedFunction("add")
-	var cpu string
+	var cpu, features string
 	cpuAttr := add.GetStringAttributeAtIndex(-1, "target-cpu")
+	featuresAttr := add.GetStringAttributeAtIndex(-1, "target-features")
 	if !cpuAttr.IsNil() {
 		cpu = cpuAttr.GetStringValue()
 	}
+	if !featuresAttr.IsNil() {
+		features = featuresAttr.GetStringValue()
+	}
 	if cpu != config.CPU() {
 		t.Errorf("target has CPU %#v but Clang makes it CPU %#v", config.CPU(), cpu)
 	}
+	if features != config.Features() {
+		if llvm.Version != "11.0.0" {
+			// This needs to be removed once we switch to LLVM 12.
+			// LLVM 11.0.0 uses a different "target-features" string than LLVM
+			// 11.1.0 for Thumb targets. The Xtensa fork is still based on LLVM
+			// 11.0.0, so we need to skip this check on that version.
+			t.Errorf("target has LLVM features %#v but Clang makes it %#v", config.Features(), features)
+		}
+	}
 }
 
 // This TestMain is necessary because TinyGo may also be invoked to run certain