testsuite: tree-ssa: fix PR98265 filename

.C is for C++ testcases and gcc.dg's dg.exp ignores .c. The test
was not being run.

gcc/testsuite/ChangeLog:
	PR ipa/98265

	* gcc.dg/tree-ssa/pr98265.C: Move to...
	* g++.dg/tree-ssa/pr98265.C: ...here.

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr98265.C b/gcc/testsuite/g++.dg/tree-ssa/pr98265.C
similarity index 100%
rename from gcc/testsuite/gcc.dg/tree-ssa/pr98265.C
rename to gcc/testsuite/g++.dg/tree-ssa/pr98265.C