Allow Zig programs to implement their own startup (_start) for ELF executables.

/home/shawn/git/zig-simd/build/lib/zig/std/special/start.zig:23:40: error: exported symbol collision: '_start'
        @export("_start", _start, .Strong);
        ^
/home/shawn/git/zig-simd/build/d.zig:1:1: note: other symbol is here
pub export fn _start() void {
^
/home/shawn/git/zig-simd/build/lib/zig/std/special/start.zig:124:35: error: root source file has no member called 'main'
    switch (@typeInfo(@typeOf(root.main).ReturnType)) {
c9937f4a2bShawn Landden committed on 9/19/2019, 3:43:00 PM· committed by Andrew Kelleyparent7ebb7ca
1 file changedLine totals unavailable