[AArch64] Parse "rng" feature flag in .arch directive

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D98566

Author: frobtech

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -2909,6 +2909,7 @@ static const struct Extension {
     {"pan-rwv", {AArch64::FeaturePAN_RWV}},
     {"ccpp", {AArch64::FeatureCCPP}},
     {"rcpc", {AArch64::FeatureRCPC}},
+    {"rng", {AArch64::FeatureRandGen}},
     {"sve", {AArch64::FeatureSVE}},
     {"sve2", {AArch64::FeatureSVE2}},
     {"sve2-aes", {AArch64::FeatureSVE2AES}},

llvm/test/MC/AArch64/directive-arch.s

@@ -17,3 +17,9 @@
 	.arch armv8-a+lse
 	casa  w5, w7, [x20]
 # CHECK:        casa    w5, w7, [x20]
+
+	.arch armv8.5-a+rng
+	mrs   x0, rndr
+	mrs   x0, rndrrs
+# CHECK:        mrs     x0, RNDR
+# CHECK:        mrs     x0, RNDRRS