When r255294 was committed, it exposed the symbols lgammal, powl,
and tgammal in libm. These functions are part of ISO/IEC 9899:1999
and their prototypes should have been moved into the appropriate
__ISO_C_VISIBLE >= 1999 section. After moving the prototypes,
remnants of r236148 can be removed.

PR: standards/191754
Reviewed by: bde