Commit cccb6c7287 has moved some function
definitions into complex.h. The functions were marked inline, but not
static, so a symbol definition was emited for them in any compilation
unit that included complex.h. If multiple such compilation units get
linked into the same binary, we get a duplicate symbol error.
Fix this by declaring the functions static inline.
libc++ disallows including LibC's complex.h in C++ mode. This means that
a C++ file cannot expect LibC's complex.h to be included, and thus
cannot use c-prefixed complex number functions. As a result,
complex.cpp is broken when libc++ has a higher include priority
than LibC.
A check for __cplusplus has been added to complex.h to warn users of
toolchains that don't use libc++.
Some header files use __BEGIN_DECLS without including sys/cdefs.h.
This causes issues for C code that compiles against these headers,
which may occur with Ports.
