re PR c++/55643 ([C++11] incorrect  "warning: variable ‘myVar’ set but not used" with an "enum class"-typed variable is casted to double for the use)

	PR c++/55643
	* expr.c (mark_exp_read): Handle FLOAT_EXPR similarly to NOP_EXPR.

	* g++.dg/warn/Wunused-var-19.C: New test.

From-SVN: r194415