* gcc.c (static_spec_functions): Add if-exists-else spec
function.
(if_exists_else_spec_function): New function.
* doc/invoke.texi: Document the if-exists-else spec function.

* config/netbsd-elf.h (NETBSD_STARTFILE_SPEC): For -static, use
"%:if-exists-else(crtbeginT%O%s crtbegin%O%s)".

From-SVN: r59480