[llvm-readobj][AArch64][ELF][PAC] 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:

- `GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_INVALID = 0`
- `GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_BAREMETAL = 1`
- `GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_LINUX = 2`

For the linux platform, output of the tools contains descriptions of
PAuth features which are enabled/disabled depending on the version
value.

Author: kovdan01

llvm/include/llvm/BinaryFormat/ELF.h

@@ -1673,6 +1673,7 @@ 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,
@@ -1690,6 +1691,13 @@ enum : unsigned {
   GNU_PROPERTY_AARCH64_FEATURE_1_PAC = 1 << 1,
 };
 
+// aarch64 PAuth platforms
+enum : unsigned {
+  GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_INVALID = 0,
+  GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_BAREMETAL = 1,
+  GNU_PROPERTY_AARCH64_FEATURE_PAUTH_PLATFORM_LINUX = 2,
+};
+
 // x86 processor feature bits.
 enum : unsigned {
   GNU_PROPERTY_X86_FEATURE_1_IBT = 1 << 0,