gdc-4.8 branch: Robert Klotzner's signals implementation doesn't work

[E.S. Quinn]

I'm not quite sure what's going on here, but I've got a build of
the current git version of the gdc-4.8 branch, and when I try to
use Robert Klotzner's proposed signals implementation (
https://github.com/phobos-x/phobosx ), it doesn't seem to work at
all; I've tried running its unit tests, and they fail pretty
early on (line 1092 of signal.d) with gdc, but they run fine with
dmd.

I've built gdc as follows:

```
Using built-in specs.
COLLECT_GCC=gdc
COLLECT_LTO_WRAPPER=/opt/gdc/libexec/gcc/x86_64-unknown-linux-gnu/4.8.2/lto-wrapper
Target: x86_64-unknown-linux-gnu
Configured with: ../gcc-4.8.2/configure --enable-languages=d
--disable-bootstrap --prefix=/opt/gdc
--with-bugurl=http://gdcproject.org/bugzilla
--enable-checking=release --enable-nls --disable-libgomp
--disable-libmudflap --disable-libquadmath --enable-libssp
--enable-multilib --enable-lto --disable-shared --disable-ld
--disable-gold
Thread model: posix
gcc version 4.8.2 (GCC)
```