re PR middle-end/20219 (Missed optimisation sin / tan --> cos)

re PR middle-end/20219 (Missed optimisation sin / tan --> cos)

	PR middle-end/20219
	* fold-const.c (fold binary) <RDIV_EXPR>: Optimize
	sin(x)/tan(x) as cos(x) and tan(x)/sin(x) as 1.0/cos(x)
	when flag_unsafe_math_optimizations is set and
	we don't care about NaNs or Infinities.

	Move x/expN(y) and x/pow(y,z) transformation into common
	flag_unsafe_math_optimizations section.

testsuite/

	* gcc.dg/builtins-20.c: Add checks for sin(x)/tan(x) and
	tan(x)/sin(x) transformations.

Co-Authored-By: Uros Bizjak <uros@kss-loka.si>
From-SVN: r107597