gcc: extend crtn workaround to alpha target

Without the change `alpha-unknown-linux-gnu` target is failing to build
`gcc`:

```
$ NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1 nix build -f ./. re2c --arg crossSystem '{ config = "alpha-unknown-linux-gnu"; }'
...
make[1]: *** No rule to make target '../../../gcc-12.3.0/libgcc/config/alpha/crti.S', needed by 'crti.o'.  Stop.
...
cc1: error: fp software completion requires '-mtrap-precision=i' [-Werror]
```

After the change it is able to produce working binaries:

```
$ NIXPKGS_ALLOW_UNSUPPORTED_SYSTEM=1 nix build -f ./. re2c --arg crossSystem '{ config = "alpha-unknown-linux-gnu"; }'
...
$ qemu-alpha ./result/bin/re2c --version
re2c 3.1

$ file result/bin/re2c
result/bin/re2c: ELF 64-bit LSB executable, Alpha (unofficial), version 1 (SYSV), dynamically linked, interpreter ...-glibc-alpha-unknown-linux-gnu-2.38-27/lib/ld-linux.so.2, for GNU/Linux 3.10.0, not stripped
```

0 files changed, 0 insertions, 0 deletions