Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

MFC r268993, r268893, r268994, plus partial r264070, r264082

Fix C++ exception handling for ARM EABI.

Just the part of r264070 that creates the FBSD_1.4 namespace in libc
is hand-applied, and then r264082 which creates the Versions.def entry
is MFC'd.

MFC 262989, 263210, 263230, 263231, 263239, 263242, 263243,

Export _libc_arm_fpu_present as a private symbol to be used by other
system libraries, for example libm.

On armv6 access both the softfloat and, when available, the vfp to get and
set the floating-point environment.

Build fenv-vfp.c with the softfp float abi. Without this gcc generates an
incorrect assembly file that doesn't allow for vfp instructions.

Only build the vfp/softfp switching code on armv6 as we don't support vfp
on anything earlier than this. This should fix the armeb and arm builds
when using gcc.

Add an optimised version of the float and double helper functions.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

When clang builds libc it may insert calls to __aeabi_* functions. Normally
this is not a problem as they are resolved by libgcc. The exception is for
the __aeabi_mem* functions. These call back into libc to the appropriate
function. This causes issues for static binaries as we only link against
libc once so there is no way for it to call into libgcc and back.

The fix for this is to include these symbols in libc but keep them hidden
so binaries use the libgcc version.

Add the required __aeabi_* functions to libc.

The floating point functions are here rather than compiler-rt because the
libc softfloat code allows us to set the rounding mode.