libc: Add __errno_location() for language binding benefits.

libc: Add __errno_location() for language binding benefits.

 Some languages have restrictions when it comes to C style TLS handling
 (thread local might be feature-gated) or simply it is inconvenient to
 add various OS specific binding wrappers just to access C errno values.

 The __errno_location() symbol provides externally callable version of
 __error() inline function.

 While there, add __WANT_NO_INLINED___ERROR guard for few python parsers
 in DPorts that are unable to parse inlined __error() code yet.