BOLT: Replace deprecated MCFixupKindInfo::FKF_IsPCRel with MCFixup::isPCRel

MCFixup::PCRel is now set at creation and the MCFixupKindInfo::FKF_IsPCRel flag
is no longer set.

Author: MaskRay

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -2557,7 +2557,7 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     else if (Fixup.getKind() ==
              MCFixupKind(AArch64::fixup_aarch64_pcrel_branch26))
       RelType = ELF::R_AARCH64_JUMP26;
-    else if (FKI.Flags & MCFixupKindInfo::FKF_IsPCRel) {
+    else if (Fixup.isPCRel()) {
       switch (FKI.TargetSize) {
       default:
         return std::nullopt;