add .gitignore entries for junk files generated by running unit tests

6 jobs for cpp11
Status Job ID Name Coverage
  Test
passed #282
Linux
clang-c++11

00:11:22

passed #284
Linux
clang-c++98

00:09:09

passed #281
Linux
gcc-c++11

00:15:58

passed #283
Linux
gcc-c++98

00:13:30

passed #285
Apple
macos-c++11

00:05:41

passed #286
Apple
macos-c++98

00:05:04