MdePkg: Check if compiler has __has_builtin before trying to use it

[bcran]

Description

When building AArch64 code, cpp gets run with the -undef flag which on Fedora 40 with gcc version 14.1.1 20240607 (Red Hat 14.1.1-5) causes __has_builtin to be undefined. When running the check for __builtin_unreachable in Base.h it causes an error "missing binary operator before token "("".

Check that we have __has_builtin before trying to use it.

• [ ] Breaking change?
  • Breaking change - Will this cause a break in build or boot behavior?
  • Examples: Add a new library class or move a module to a different repo.
• [ ] Impacts security?
  • Security - Does the change have a direct security impact?
  • Examples: Crypto algorithm change or buffer overflow fix.
• [ ] Includes tests?
  • Tests - Does the change include any explicit test code?
  • Examples: Unit tests or integration tests.

How This Was Tested

Built code on Fedora Server 40 before and after this change and verified the build now succeeds.

Integration Instructions

N/A

[lgao4]

The change is good. Please first check what CI issue here.