On FreeBSD, perl isn't in /usr/bin, its in /usr/local/bin or
elsewhere in the path.
Like storage/{maria/unittest/,}ma_test_* , we use /usr/bin/env to
find perl and run it.
- add process-gcov-annotations.pl script that processes .gcov files
according to purecov annotations in source code
- add --gcov-src-dir=subdir option to mysql-test-run so that one can
do gcov processing only for source files in a certain directory.