[PAC][lld] Support -z nopac-plt flag (#132973)

Support `-z nopac-plt` so it's possible to cancel previous `-z pac-plt`.

Author: kovdan01

lld/ELF/Driver.cpp

@@ -1575,7 +1575,7 @@ static void readConfigs(Ctx &ctx, opt::InputArgList &args) {
   ctx.arg.zNodlopen = hasZOption(args, "nodlopen");
   ctx.arg.zNow = getZFlag(args, "now", "lazy", false);
   ctx.arg.zOrigin = hasZOption(args, "origin");
-  ctx.arg.zPacPlt = hasZOption(args, "pac-plt");
+  ctx.arg.zPacPlt = getZFlag(args, "pac-plt", "nopac-plt", false);
   ctx.arg.zRelro = getZFlag(args, "relro", "norelro", true);
   ctx.arg.zRetpolineplt = hasZOption(args, "retpolineplt");
   ctx.arg.zRodynamic = hasZOption(args, "rodynamic");

lld/test/ELF/aarch64-feature-pac.s

@@ -8,10 +8,15 @@
 ## We do not add PAC support when the inputs don't have the .note.gnu.property
 ## field.
 
-# RUN: ld.lld %tno.o %t3.o --shared -o %tno.so
-# RUN: llvm-objdump --no-print-imm-hex -d --mattr=+v8.3a --no-show-raw-insn %tno.so | FileCheck --check-prefix=NOPAC %s
-# RUN: llvm-readelf -x .got.plt %tno.so | FileCheck --check-prefix SOGOTPLT %s
-# RUN: llvm-readelf --dynamic-table %tno.so | FileCheck --check-prefix NOPACDYN %s
+# RUN: ld.lld %tno.o %t3.o --shared -o %tno1.so
+# RUN: llvm-objdump --no-print-imm-hex -d --mattr=+v8.3a --no-show-raw-insn %tno1.so | FileCheck --check-prefix=NOPAC %s
+# RUN: llvm-readelf -x .got.plt %tno1.so | FileCheck --check-prefix SOGOTPLT %s
+# RUN: llvm-readelf --dynamic-table %tno1.so | FileCheck --check-prefix NOPACDYN %s
+
+# RUN: ld.lld %tno.o %t3.o --shared -o %tno2.so -z pac-plt -znopac-plt
+# RUN: llvm-objdump --no-print-imm-hex -d --mattr=+v8.3a --no-show-raw-insn %tno2.so | FileCheck --check-prefix=NOPAC %s
+# RUN: llvm-readelf -x .got.plt %tno2.so | FileCheck --check-prefix SOGOTPLT %s
+# RUN: llvm-readelf --dynamic-table %tno2.so | FileCheck --check-prefix NOPACDYN %s
 
 # NOPAC: 00000000000102b8 <func2>:
 # NOPAC-NEXT:    102b8: bl      0x102f0 <func3@plt>