Before 1.7.5, we were setting -fno-exceptions etc on CXXFLAGS. In 1.7.6
we set it as CPPFLAGS. Try fixing. Also, I'm fairly sure it's safe to
set these unconditionally.

Fixes https://github.com/harfbuzz/harfbuzz/issues/880 (or so I hope)

Fixes https://github.com/harfbuzz/harfbuzz/issues/865

Fixes https://github.com/harfbuzz/harfbuzz/issues/901

Fixes https://github.com/harfbuzz/harfbuzz/issues/901

For pre-C99 compilers that do not support round(), we need to have a
simplistic implementation for it, when it is not detected during build
configuration, either via CMake or autotools, by using floor() and
ceil(), which are provided in the pre-C99 compilers.

Please see discussion at commit 86a0ac28 for more details for re-adding
this patch.

...on static builds.

[subset] Check for the Null table and not nullptr to detect failure to find a table in glyf accelerator.

But keep use of cmake idiomatic way of making inlines hidden