[PAC][llvm-readobj][AArch64][ELF] Support GNU_PROPERTY_AARCH64_FEATURE_PAUTH

This adds support for `GNU_PROPERTY_AARCH64_FEATURE_PAUTH` feature
handling in llvm-readobj and llvm-readelf. The following constants for
supported platforms are also introduced:

- `AARCH64_PAUTH_PLATFORM_INVALID = 0x0`
- `AARCH64_PAUTH_PLATFORM_BAREMETAL = 0x1`
- `AARCH64_PAUTH_PLATFORM_LLVM_LINUX = 0x10000002`

For the llvm_linux platform, output of the tools contains descriptions of
PAuth features which are enabled/disabled depending on the version value.
Version value bits correspond to the following `LangOptions`:

- bit 0: `PointerAuthIntrinsics`;
- bit 1: `PointerAuthCalls`;
- bit 2: `PointerAuthReturns`;
- bit 3: `PointerAuthAuthTraps`;
- bit 4: `PointerAuthVTPtrAddressDiscrimination`;
- bit 5: `PointerAuthVTPtrTypeDiscrimination`;
- bit 6: `PointerAuthInitFini`.

Author: kovdan01

llvm/include/llvm/BinaryFormat/ELF.h

@@ -1738,6 +1738,7 @@ enum : unsigned {
   GNU_PROPERTY_STACK_SIZE = 1,
   GNU_PROPERTY_NO_COPY_ON_PROTECTED = 2,
   GNU_PROPERTY_AARCH64_FEATURE_1_AND = 0xc0000000,
+  GNU_PROPERTY_AARCH64_FEATURE_PAUTH = 0xc0000001,
   GNU_PROPERTY_X86_FEATURE_1_AND = 0xc0000002,
 
   GNU_PROPERTY_X86_UINT32_OR_LO = 0xc0008000,
@@ -1756,6 +1757,13 @@ enum : unsigned {
   GNU_PROPERTY_AARCH64_FEATURE_1_GCS = 1 << 2,
 };
 
+// aarch64 PAuth platforms.
+enum : unsigned {
+  AARCH64_PAUTH_PLATFORM_INVALID = 0x0,
+  AARCH64_PAUTH_PLATFORM_BAREMETAL = 0x1,
+  AARCH64_PAUTH_PLATFORM_LLVM_LINUX = 0x10000002,
+};
+
 // x86 processor feature bits.
 enum : unsigned {
   GNU_PROPERTY_X86_FEATURE_1_IBT = 1 << 0,