stdlib/tst-strtod-overflow: Bump timeout up yet

This test case is very, especially on targets using soft-float or QEMU
(where soft-float is used internally), and appears to be the only such
outlier.  Therefore rather than requiring to have TIMEOUTFACTOR set
large enough globally, bump up the local scaling factor instead.

	* stdlib/tst-strtod-overflow.c (TIMEOUT): Bump up to 30.
powerpc: Remove dummy hp-timing.h

It's the same as the generic dummy version.
Removing HP_TIMING_ZERO as unused
Removing HP_TIMING_ACCUM as unused
Remove HP_TIMING_DIFF_INIT and dl_hp_timing_overhead

Without HP_TIMING_ACCUM, dl_hp_timing_overhead is write-only.
If we remove it, there's no point in HP_TIMING_DIFF_INIT either.
Unify hp-timing implementations

Provide an hp-timing-common.h for ports to use.
aarch64: Add hp-timing.h
Always provide HP_SMALL_TIMING_AVAIL
Rely on HP_TIMING_AVAIL implies HP_SMALL_TIMING_AVAIL
Changelog for last 8 patches
alpha: Remove round and roundf implementations

Two bugs in these implementations: First is that the add of 0.5
was not done in chopped rounding mode (easily fixable).  Second
is that the method generates incorrect inexact exceptions for
small integral values (not easily fixable).
alpha: Fix lround implementations

Use chopped rounding to add 0.5.
alpha: Implement math_opt_barrier and math_force_eval
alpha: Remove nearbyint and nearbyintf implementations

The original implementation was written for EV5, which does not
record inexact in the status register for /SU (but no /I) insns.
But EV6 does record the inexact status; the lack of /I simply
means that the exception is suppressed.

Adding feholdexcept becomes the bulk of the overhead, so we might
as well use the default implementation.