Shut up warnings

Dependencies

• [2] G7LMCJH5 Add some gitignores
• [*] GBCPEGYC Add a .gitignore
• [*] FV2M6MOT hydra: use autoconf/-make
• [*] Y6H7Y3OT Capture the path to `guile', when available.

Change contents

• edit in .gitignore at line 34
  [2.108]
  + hydra-config.h

  + hydra-config.h.in
• edit in configure.ac at line 89
  [6.272]

  [6.272]
  +

  + AC_CONFIG_HEADER([hydra-config.h])