[AArch64][AsmParser] Add rcpc support in .arch_extension

[vhscampos]

Summary

AArch64 does not support enabling rcpc via .arch_extension in assembly.
GCC, on the other hand, does.

This patch adds 'rcpc' as a valid value to .arch_extension handling.

[ostannard]

LGTM

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

const FeatureBitset Features;
     {"ras", {AArch64::FeatureRAS}},
     {"lse", {AArch64::FeatureLSE}},
     {"predres", {AArch64::FeaturePredRes}},
     {"ccdp", {AArch64::FeatureCacheDeepPersist}},
     {"mte", {AArch64::FeatureMTE}},
     {"tlb-rmi", {AArch64::FeatureTLB_RMI}},
     {"pan-rwv", {AArch64::FeaturePAN_RWV}},
     {"ccpp", {AArch64::FeatureCCPP}},
+    {"rcpc", {AArch64::FeatureRCPC}},
     {"sve", {AArch64::FeatureSVE}},
     {"sve2", {AArch64::FeatureSVE2}},
     {"sve2-aes", {AArch64::FeatureSVE2AES}},
     {"sve2-sm4", {AArch64::FeatureSVE2SM4}},
     {"sve2-sha3", {AArch64::FeatureSVE2SHA3}},
     {"sve2-bitperm", {AArch64::FeatureSVE2BitPerm}},
     // FIXME: Unsupported extensions
     {"pan", {}},

llvm/test/MC/AArch64/directive-arch_extension-negative.s

 at s1e1wp, x2
 // CHECK: error: AT S1E1WP requires pan-rwv
 // CHECK-NEXT: at s1e1wp, x2
 
 .arch_extension noccpp
 dc cvap, x7
 // CHECK: error: DC CVAP requires ccpp
 // CHECK-NEXT: dc cvap, x7
+
+.arch_extension norcpc
+ldapr x0, [x1]
+// CHECK: error: instruction requires: rcpc
+// CHECK-NEXT: ldapr x0, [x1]

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

 
 .arch_extension pan-rwv
 at s1e1wp, x2
 // CHECK: at s1e1wp, x2
 
 .arch_extension ccpp
 dc cvap, x7
 // CHECK: dc cvap, x7
+
+.arch_extension rcpc
+ldapr x0, [x1]
+// CHECK: ldapr x0, [x1]