Disable -fexceptions compiler flag.

When -fexceptions is used the library needs to link against
libgcc_s.so for the stack unwind implementation.

Linking against libgcc_s.so is however somewhat problematic
due to .so versioning issues. The compiler provides libgcc_s.so,
which in turn links against the system glibc.so, specifically,
linking against a version of glibc.so that is later the version
we wish to provide compatibility for.

The options here are to compile our own version of libgcc_s.so,
which links against an appropriate version of glibc, however
this effectively requires supporting our own toolchain which
is, at this stage of the project, undesirable.

Instead we work around the problem by avoiding any code that
requires the unwind code found in libgcc_s.so. This is unlikely
to work in the long term, but is the most effective approach
right now.