riscv: std.fmt.format running

- implements `airSlice`, `airBitAnd`, `airBitOr`, `airShr`.

- got a basic design going for the `airErrorName` but for some reason it simply returns
empty bytes. will investigate further.

- only generating `.got.zig` entries when not compiling an object or shared library

- reduced the total amount of ops a mnemonic can have to 3, simplifying the logic

test/behavior/memset.zig

@@ -7,7 +7,6 @@ test "@memset on array pointers" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest;
     if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
 
     try testMemsetArray();
     try comptime testMemsetArray();
@@ -167,7 +166,6 @@ test "zero keys with @memset" {
     if (builtin.zig_backend == .stage2_arm) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_sparc64) return error.SkipZigTest; // TODO
     if (builtin.zig_backend == .stage2_spirv64) return error.SkipZigTest;
-    if (builtin.zig_backend == .stage2_riscv64) return error.SkipZigTest;
 
     const Keys = struct {
         up: bool,