Target specific optimization control.

This allows one to set a semi-colon separated list of regular
expressions in the environment variable PX4_NO_OPTIMIZATION
to control which (cmake generated) targets should be compiled
without optimization.

Suppressing optimization can be necessary for debugging in
a debugger, especially when trying to step through the code
or needing to print variables that otherwise are optimized out.

EXAMPLE

export PX4_NO_OPTIMIZATION="px4;^modules__uORB;^modules__systemlib$"

will result in the following messages during cmake configuration:

[...]
-- Disabling optimization for target 'platforms__posix__px4_layer'
because it matches the regexp 'px4' in env var PX4_NO_OPTIMIZATION
-- Disabling optimization for target 'modules__systemlib' because it
matches the regexp '^modules__systemlib$' in env var PX4_NO_OPTIMIZATION
-- Disabling optimization for target 'modules__uORB' because it matches
the regexp '^modules__uORB' in env var PX4_NO_OPTIMIZATION
-- Disabling optimization for target 'examples__px4_simple_app' because
it matches the regexp 'px4' in env var PX4_NO_OPTIMIZATION
-- Disabling optimization for target 'modules__uORB__uORB_tests' because
it matches the regexp '^modules__uORB' in env var PX4_NO_OPTIMIZATION
-- Disabling optimization for target 'px4' because it matches the regexp
'px4' in env var PX4_NO_OPTIMIZATION

Note that a list of all (currently used) target names can be printed
with the following command line from within the required build directory:

find . -wholename '*/CMakeFiles/*.dir/flags.make' | xargs dirname | xargs basename -a | sort -u | sed -e 's/.dir$//'