[ng] check: minor refactoring (reorder code)

[ng] check: minor refactoring (reorder code)

This is just movement and minor reorganization of code; no semantic
change is intended.

* lib/am/check.am (am__sh_e_setup): Moved ...
* lib/am/header-vars.am (am__sh_e_setup): ... here.
* lib/am/check.am (am__check_pre, am__common_driver_flags): Removed,
their contents merged ...
* lib/am/check2.am [%?FIRTS%] (am__runtest): ... into this.  Other
related whitespace and indentation changes since we are at it.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>