Fix linker issue

[svelterust]

Figure out why c.VBlankIntrWait() from gba_systemcalls.h doesn't work.

zig-gba on  master [!] via ↯ v0.9.1 ❯ zig build
/opt/devkitpro/devkitARM/bin/../lib/gcc/arm-none-eabi/12.1.0/../../../../arm-none-eabi/bin/ld: zig-out/zig-gba.o: in function `main':
/home/odd/source/zig/zig-gba/src/main.zig:11: undefined reference to `VBlankIntrWait'
collect2: error: ld returned 1 exit status
The following command exited with error code 1 (expected 0):
cd /home/odd/source/zig/zig-gba && /opt/devkitpro/devkitARM/bin/arm-none-eabi-gcc -g -mthumb -mthumb-interwork -Wl,-Map,zig-out/zig-gba.map -specs=/opt/devkitpro/devkitARM/arm-none-eabi/lib/gba.specs zig-out/zig-gba.o -L/opt/devkitpro/libgba/lib -L/opt/devkitpro/portlibs/libgba/lib -lgba -o zig-out/zig-gba.elf 
error: UnexpectedExitCode
/usr/lib/zig/std/os.zig:2714:19: 0x2a61e2 in std.os.readlinkZ (build)
        .INVAL => return error.NotLink,
                  ^
/usr/lib/zig/std/os.zig:2693:9: 0x2a6f32 in std.os.readlink (build)
        return readlinkZ(&file_path_c, out_buffer);
        ^
/usr/lib/zig/std/os.zig:2418:19: 0x294dbb in std.os.mkdiratZ (build)
        .EXIST => return error.PathAlreadyExists,
                  ^
/usr/lib/zig/std/os.zig:2380:9: 0x294ca3 in std.os.mkdirat (build)
        return mkdiratZ(dir_fd, &sub_dir_path_c, mode);
        ^
/usr/lib/zig/std/fs.zig:1261:9: 0x294b96 in std.fs.Dir.makeDir (build)
        try os.mkdirat(self.fd, sub_path, default_new_dir_mode);
        ^
/usr/lib/zig/std/os.zig:2418:19: 0x294dbb in std.os.mkdiratZ (build)
        .EXIST => return error.PathAlreadyExists,
                  ^
/usr/lib/zig/std/os.zig:2380:9: 0x294ca3 in std.os.mkdirat (build)
        return mkdiratZ(dir_fd, &sub_dir_path_c, mode);
        ^
/usr/lib/zig/std/fs.zig:1261:9: 0x294b96 in std.fs.Dir.makeDir (build)
        try os.mkdirat(self.fd, sub_path, default_new_dir_mode);
        ^
/usr/lib/zig/std/build/RunStep.zig:238:17: 0x2adc80 in std.build.RunStep.make (build)
                return error.UnexpectedExitCode;
                ^
/usr/lib/zig/std/build.zig:3201:9: 0x295fce in std.build.Step.make (build)
        try self.makeFn(self);
        ^
/usr/lib/zig/std/build.zig:502:9: 0x29466c in std.build.Builder.makeOneStep (build)
        try s.make();
        ^
/usr/lib/zig/std/build.zig:496:17: 0x294618 in std.build.Builder.makeOneStep (build)
                return err;
                ^
/usr/lib/zig/std/build.zig:496:17: 0x294618 in std.build.Builder.makeOneStep (build)
                return err;
                ^
/usr/lib/zig/std/build.zig:496:17: 0x294618 in std.build.Builder.makeOneStep (build)
                return err;
                ^
/usr/lib/zig/std/build.zig:457:13: 0x285901 in std.build.Builder.make (build)
            try self.makeOneStep(s);
            ^
/usr/lib/zig/std/special/build_runner.zig:213:21: 0x27a384 in main (build)
            else => return err,
                    ^
error: the following build command failed with exit code 1:
/home/odd/source/zig/zig-gba/zig-cache/o/88764fb0e286c9b9bc25dc7c887d9e5e/build /usr/bin/zig /home/odd/source/zig/zig-gba /home/odd/source/zig/zig-gba/zig-cache /home/odd/.cache/zig