build: fix spurious mksnapshot crashes for good

A variety of gcc bugs made mksnapshot crash with either a segmentation fault
or a 'pure virtual method callled' run-time error.

After much wailing and gnashing of teeth I managed to deduce that the bugs
show up when:

  1. gcc 4.5.2 for i386-pc-solaris2.11 is used and -fstrict-aliasing is
     enabled, or

  2. gcc version 4.4.6 for x86_64-redhat-linux is used and
     -ffunction-sections -finline-functions at -O2 or higher is enabled

Therefore, disable -ffunction-sections and -fdata-sections unconditionally
and disable -fstrict-aliasing only on Solaris.

The -ffunction-sections and -fdata-sections switches were nonsense anyway
because we don't link with -Wl,--gc-sections.