Update the instances of checks for architectures to be more broad for different
spellings of the architecture macro. Certain targets use `_M_ARM` and others
use `__arm__`. Similarly, arm64/aarch64 has `_M_ARM64`, `__arm64__` and
`__aarch64__` as spellings. This just mechanically goes through and encodes the
various spellings.
Take the opportunity to replace some raw checks with `defined` checks which
avoids a pedantic warning due to the undefined macro when performing the check
as the preprocessor may warn about an undefined condition evaluating to `0`.
The quad precision support in visual studio does not support
the operations which clang will sometimes lower. These currently
generate code using GNU extensions. Add additional stubs for math
routines on Windows. This allows the standard library to build in
debug mode.
Move the duplicated compiler-rt support routines into its own source
file. This will need to be expanded for Windows. As on Linux, there
are certain builtin routines which are not available from the standard
runtime and need to be augmented for now.
