compiler: replace some math operation bodies with fast intrinsics

Instead of changing the calls, replace the function bodies themselves.
This is useful for a number of reasons, see
https://github.com/tinygo-org/tinygo/pull/2920 for more information.

I have removed the math intrinsics tests because they are no longer
useful. Instead, I think `tinygo test math` should suffice.

compiler/compiler_test.go

@@ -27,12 +27,6 @@ type testCase struct {
 func TestCompiler(t *testing.T) {
 	t.Parallel()
 
-	// Determine LLVM version.
-	llvmMajor, err := strconv.Atoi(strings.SplitN(llvm.Version, ".", 2)[0])
-	if err != nil {
-		t.Fatal("could not parse LLVM version:", llvm.Version)
-	}
-
 	// Determine which tests to run, depending on the Go and LLVM versions.
 	tests := []testCase{
 		{"basic.go", "", ""},
@@ -47,14 +41,8 @@ func TestCompiler(t *testing.T) {
 		{"goroutine.go", "wasm", "asyncify"},
 		{"goroutine.go", "cortex-m-qemu", "tasks"},
 		{"channel.go", "", ""},
-		{"intrinsics.go", "cortex-m-qemu", ""},
-		{"intrinsics.go", "wasm", ""},
 		{"gc.go", "", ""},
 	}
-	if llvmMajor >= 12 {
-		tests = append(tests, testCase{"intrinsics.go", "cortex-m-qemu", ""})
-		tests = append(tests, testCase{"intrinsics.go", "wasm", ""})
-	}
 
 	for _, tc := range tests {
 		name := tc.file