add error messages for mask and enable #26

Job	Run time
7.0/ubuntu-20.04/gcc/default/	1m 30s
7.0/ubuntu-20.04/gcc/static/	1m 29s
3.15/ubuntu-20.04/gcc/default/	1m 10s
3.14/ubuntu-20.04/gcc/default/	1m 51s
7.0/ubuntu-20.04/gcc/static/CMD_CXXFLAGS=-std=c++11	1m 27s
7.0/ubuntu-20.04/clang/default/CMD_CXXFLAGS=-std=c++11	1m 21s
7.0/ubuntu-20.04/gcc/default4.10/	2m 5s
7.0/ubuntu-20.04/gcc/default4.9/	1m 45s
7.0/ubuntu-20.04/gcc-8/default/	1m 35s
7.0/ubuntu-20.04/clang/default/	1m 27s
7.0/ubuntu-latest/gcc/default/	1m 18s
	16m 58s

Provide feedback