amd64 crt1: Explicitly use a PLT entry for main in the PIC case.

[jhb]

Summary

This ensures GNU as generates a R_X86_64_PLT32 relocation instead of
R_X86_64_32.

Fixes: c969310c992a csu: Implement _start using as to satisfy unwinders on x86_64

[jhb]

This fixes linking dynamic binaries again with GCC 12.

[jlduran]

Thank you!
I also had to add:

LDFLAGS+=       -Wl,-znoexecstack

to secure/lib/libcrypto/**/**/Makefile.

EDIT: https://github.com/freebsd/freebsd-src/pull/800

[jhb]

In D41101#935894, @jlduran_gmail.com wrote:

Thank you!
I also had to add:

LDFLAGS+=       -Wl,-znoexecstack

to secure/lib/libcrypto/**/**/Makefile.

EDIT: https://github.com/freebsd/freebsd-src/pull/800

I have a separate review for this: D41102