Use eval so that $cmake_opts is properly parsed

Without eval bash inserts single quotes and breaks parameters passed
if they have quotes in the parameters. For example
`-D CMAKE_CXX_FLAGS="-fPIC -std=gnu++11"`

Issue: RELENG-1075
Change-Id: I77046a7edc0516f0ae28dd2b8cd2c8994ad5079e
Signed-off-by: Thanh Ha <thanh.ha@linuxfoundation.org>