Move closer to the standard autotools idiom. (#3187)

* 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`.

src/main.c

@@ -35,8 +35,6 @@ extern void jv_tsd_dtoa_ctx_init();
 #include "jq.h"
 #include "jv_alloc.h"
 #include "util.h"
-#include "src/version.h"
-#include "src/config_opts.inc"
 
 int jq_testsuite(jv lib_dirs, int verbose, int argc, char* argv[]);