[ARM] Add command-line option for SB

SB (Speculative Barrier) is only mandatory from 8.5
onwards but is optional from Armv8.0-A. This patch adds a command
line option to enable SB, as it was previously only possible to
enable by selecting -march=armv8.5-a.

This patch also renames FeatureSpecRestrict to FeatureSB.

Reviewed By: olista01, LukeCheeseman

Differential Revision: https://reviews.llvm.org/D55990

llvm-svn: 350299
diff --git a/llvm/unittests/Support/TargetParserTest.cpp b/llvm/unittests/Support/TargetParserTest.cpp
index 7fc51ae..3676dee 100644
--- a/llvm/unittests/Support/TargetParserTest.cpp
+++ b/llvm/unittests/Support/TargetParserTest.cpp
@@ -584,7 +584,8 @@
                               {"iwmmxt", "noiwmmxt", nullptr, nullptr},
                               {"iwmmxt2", "noiwmmxt2", nullptr, nullptr},
                               {"maverick", "maverick", nullptr, nullptr},
-                              {"xscale", "noxscale", nullptr, nullptr}};
+                              {"xscale", "noxscale", nullptr, nullptr},
+                              {"sb", "nosb", "+sb", "-sb"}};
 
   for (unsigned i = 0; i < array_lengthof(ArchExt); i++) {
     EXPECT_EQ(StringRef(ArchExt[i][2]), ARM::getArchExtFeature(ArchExt[i][0]));