cmd/compile: add pure Go math/big functions to TestIntendedInlining

Change-Id: Id29a9e48a09965e457f923a0ff023722b38b27ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/165157
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/inl_test.go

@@ -144,6 +144,9 @@ func TestIntendedInlining(t *testing.T) {
 		},
 		"math/big": {
 			"bigEndianWord",
+			// The following functions require the math_big_pure_go build tag.
+			"addVW",
+			"subVW",
 		},
 	}
 
@@ -202,7 +205,7 @@ func TestIntendedInlining(t *testing.T) {
 		}
 	}
 
-	args := append([]string{"build", "-a", "-gcflags=all=-m -m"}, pkgs...)
+	args := append([]string{"build", "-a", "-gcflags=all=-m -m", "-tags=math_big_pure_go"}, pkgs...)
 	cmd := testenv.CleanCmdEnv(exec.Command(testenv.GoToolPath(t), args...))
 	pr, pw := io.Pipe()
 	cmd.Stdout = pw