* data/push.c: Add CPP guards around push parser declarations in both

* data/push.c: Add CPP guards around push parser declarations in both
the header and the code file.
In the code file, move the push parser declarations to the same place
they appear in the header file.
Clean up the M4 some, especially the inconsistent underquoting in
some b4_c_function_def and b4_c_function_decl uses.