testsuite/rs6000: Move pr83660.C to g++.target

Move pr83660.C to g++.target.  As comment #3 of PR83660,
rename it to c isn't one option.

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/pr83660.C: Moved to...
	* g++.target/powerpc/pr83660.C: ...here.

diff --git a/gcc/testsuite/gcc.target/powerpc/pr83660.C b/gcc/testsuite/g++.target/powerpc/pr83660.C
similarity index 100%
rename from gcc/testsuite/gcc.target/powerpc/pr83660.C
rename to gcc/testsuite/g++.target/powerpc/pr83660.C