CTest: Fix typo in CTEST_PARALLEL_LEVEL documentation
CTest: Read CTEST_PARALLEL_LEVEL from environment

If no explicit "-j <n>" option is given on the command line then read
the parallel level from an environment variable.
Merge topic 'ctest-parallel-env' into next

5d92c3d CTest: Fix typo in CTEST_PARALLEL_LEVEL documentation
string: Add MAKE_C_IDENTIFIER subcommand
Merge topic 'ctest-parallel-env' into next

db43502 CTest: Read CTEST_PARALLEL_LEVEL from environment
Merge topic 'string-MAKE_C_IDENTIFIER-subcommand' into next

0ab50ae string: Add MAKE_C_IDENTIFIER subcommand