Declare all environmental version identifiers relating to the target CPU
using the function
builtin_version, which takes a string representing
the name of the version. Version identifiers predefined by this hook apply
to all modules that are being compiled and imported.
TARGET_D_CPU_VERSIONS, but is used for versions
relating to the target operating system.
Returns the size of the data structure used by the target operating system
for critical sections and monitors. For example, on Microsoft Windows this
would return the
sizeof(CRITICAL_SECTION), while other platforms that
implement pthreads would return