test/codegen: port math/bits.RotateLeft tests to codegen

Only RotateLeft{64,32} were tested, and just for ppc64. This CL adds
tests for RotateLeft{64,32,16,8} on arm64 and amd64/386, for the cases
where the calls are actually instrinsified.

RotateLeft tests (the last ones for math/bits functions) are deleted
from asm_test.

This CL also adds a space between the "//" and the arch name in the
comments, to uniform this file to the style used in all the other
files.

Change-Id: Ifc2a27261d70bcc294b4ec64490d8367f62d2b89
Reviewed-on: https://go-review.googlesource.com/99596
Reviewed-by: Giovanni Bajo <rasky@develer.com>

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

@@ -259,10 +259,9 @@ var allAsmTests = []*asmTests{
 		tests: linuxMIPS64Tests,
 	},
 	{
-		arch:    "ppc64le",
-		os:      "linux",
-		imports: []string{"math/bits"},
-		tests:   linuxPPC64LETests,
+		arch:  "ppc64le",
+		os:    "linux",
+		tests: linuxPPC64LETests,
 	},
 	{
 		arch:  "amd64",
@@ -1701,23 +1700,6 @@ var linuxPPC64LETests = []*asmTest{
 		`,
 		pos: []string{"\tROTL\t"},
 	},
-	{
-		fn: `
-		func f10(a uint32) uint32 {
-			return bits.RotateLeft32(a, 9)
-		}
-		`,
-		pos: []string{"\tROTLW\t"},
-	},
-	{
-		fn: `
-		func f11(a uint64) uint64 {
-			return bits.RotateLeft64(a, 37)
-		}
-		`,
-		pos: []string{"\tROTL\t"},
-	},
-
 	{
 		// check that stack store is optimized away
 		fn: `