ext: Update fputils to rev 52b6190b4e

This changeset updates the external library to git revision
52b6190b4e. This update includes changes that fix compilation errors
on old gcc versions and fixes to test a case that affect ICC.
scons, kvm: Check for the presence of POSIX timers

The kvm-based CPU module requires support for POSIX timers. This
changeset adds a check for POSIX timers and ensures that gem5 is
linked with librt if necessary. KVM support is disabled if POSIX
timers are not supported by the host. This fixes a compilation issue
for some glibc versions where clock_nanosleep and timer_create are in
different libraries.
stats: Update x86 stats after x87 fixes

The updates to the x87 caused the stats for several regressions to
change. This was mainly caused by the addition of a working 32-bit and
80-bit FP load instruction and xsave support.
ext: Fix fputils compiler flags to ensure ISO C99

The fp code relies on C99, and depending on gcc version, the default
is to use c89. This patch adds -std=c99 when using gcc to ensure the
code is compiled in ISO C99 mode.
kvm: Only include KVM support for supported kernels

This patch adds a check to ensure that the KVM API provided by the
running kernel is what we are expecting.