[libc] Enable ifunc support in static startup (#182841)
Resolves ifunc targets before `main()` runs in static libc
This enables static binaries to use ifunc-based dispatch during early
process startup, so optimized implementations can be selected based on
CPU features. Without this relocation step in startup, those targets are
not ready when program code begins executing.
This change:
- adds IRELATIVE relocation handling for x86_64, AArch64, ARMv7 and RISC-V,
- reads `AT_HWCAP` / `AT_HWCAP2` from auxv and passes them to resolvers
where required (notably AArch64),
- runs IRELATIVE processing after base-address discovery and before TLS
setup,
- adds integration tests for both the ifunc path and the no-ifunc path,
- Changed the load bias type for ptrdiff_t to intptr_t to align with
IRELATIVE handling, which uses intptr_t for load bias calculations.
