* Create `src/config.h` instead of passing everything on the compiler
command line.
* To reduce the magnitude of this change, add `--include src/config.h`
to CFLAGS instead of adding `#include "src/config.h"` at the top of
each source file. Not all compilers support this, but I don't think
we care about anything other than gcc and clang at this point.
* Rather than generate `src/config_opts.inc`, emit `JQ_CONFIG` directly
into `src/config.h`.
* Rather than generate `src/version.h`, define `JQ_VERSION` as an alias
for the standard `PACKAGE_VERSION`.
* Improve reliability of NO_COLOR tests.
Use `env` to ensure that `NO_COLOR` is set to the desired value
regardless of any initialization that may occur when `script`
forks a shell to run jq in.
Note that `env -u` is not portable, so there is no good solution
for the first test case.
* Always use /bin/sh, not the user's login shell.
Dag-Erling Smørgrav