target: Rename sparcv9 -> sparc64

Rename all references of sparcv9 to sparc64, to make Zig align more with
other projects. Also, added new function to convert glibc arch name to Zig
arch name, since it refers to the architecture as sparcv9.

This is based on the suggestion by @kubkon in PR 11847.
(https://github.com/ziglang/zig/pull/11487#pullrequestreview-963761757)

lib/c.zig

@@ -625,7 +625,7 @@ fn clone() callconv(.Naked) void {
                 \\  sc
             );
         },
-        .sparcv9 => {
+        .sparc64 => {
             // __clone(func, stack, flags, arg, ptid, tls, ctid)
             //           i0,    i1,    i2,  i3,   i4,  i5,   sp
             // syscall(SYS_clone, flags, stack, ptid, tls, ctid)