Many warnings in autoconf

[sipa]

When running autogen:

Makefile.am:45: warning: source file 'src/secp256k1.c' is in a subdirectory,
Makefile.am:45: but option 'subdir-objects' is disabled
automake: warning: possible forward-incompatibility.
automake: At least a source file is in a subdirectory, but the 'subdir-objects'
automake: automake option hasn't been enabled.  For now, the corresponding output
automake: object file(s) will be placed in the top-level directory.  However,
automake: this behaviour will change in future Automake versions: they will
automake: unconditionally cause object files to be placed in the same subdirectory
automake: of the corresponding sources.
automake: You are advised to start using 'subdir-objects' option throughout your
automake: project, to avoid future incompatibilities.
Makefile.am:62: warning: source file 'src/bench_inv.c' is in a subdirectory,
Makefile.am:62: but option 'subdir-objects' is disabled
Makefile.am:56: warning: source file 'src/bench_recover.c' is in a subdirectory,
Makefile.am:56: but option 'subdir-objects' is disabled
Makefile.am:59: warning: source file 'src/bench_sign.c' is in a subdirectory,
Makefile.am:59: but option 'subdir-objects' is disabled
Makefile.am:53: warning: source file 'src/bench_verify.c' is in a subdirectory,
Makefile.am:53: but option 'subdir-objects' is disabled
Makefile.am:70: warning: source file 'src/tests.c' is in a subdirectory,
Makefile.am:70: but option 'subdir-objects' is disabled

[sipa]

Ping @theuni.

[theuni]

looking now.