Re: x86-64: Estimate output section layout before sizing dynamic sections

Commit 73ab3b9825 results in a warning compiling eelf_x86_64_sol2.c,
breaking --enable-targets=all builds.
warning: ‘elf_x86_64_before_allocation’ defined but not used

Fix this by hooking up the chain of before_allocation functions, so
x86_64-solaris2 calls elf_x86_64_before_allocation, while
sparc64-solaris2 calls gldelf64_sparc_sol2_before_allocation.