[clang] Using std::complex suppresses warnings from -Whigher-precision-for-complex-division

[Maetveis]

The -Whigher-precision-for-complex-division emitted when -fcomplex-arithmetic=promoted option is used and the target does not support a higher precison type is not emitted:

• for C++ std::complex divisions (instead of C _Complex)
• when including <complex> from libstdc++ (after [Clang][Sema] Fix -Whigher-precision-for-complex-division #131477), even if using _Complex
• when including <complex> from libc++ and instantiating the templated std::complex division. (Compiler explorer link) even if using _Complex

libstdc++ does not suppress the warning before #131477 because its using /= which is fixed by #131477

[Maetveis]

-Whigher-precision-for-complex-division is emitted at most once, probably to reduce on the amount of noise. However if this is in a system header (e.g. <complex>) than it is ignored, so the user does not see it, and further diagnostics are not emitted.