libexpr's symbol table has changed

Dependencies

• [2] NDJ6PZB7 * Fix symbol to look for.
• [3] 2KJFOYGS hydra: Actually check for Nix in `configure'.
• [4] FJILMA6G configure: Preserve the user's $CPPFLAGS and $LDFLAGS.
• [5] HX4QYOYA add first evaluations tests
• [6] KBONEPPH configure: Pass `-L/to/nix' as $LDFLAGS, not $LIBS.
• [7] WR6LRCAC oops, committed too much
• [*] FV2M6MOT hydra: use autoconf/-make

Change contents

• replacement in configure.ac at line 70
  [3.248]→[2.0:69](∅→∅)
  − AC_CHECK_LIB([expr], [_ZN3nix9EvalState17parseExprFromFileESs], [:],
  [3.248]

  [3.74]
  + AC_CHECK_LIB([expr], [_ZN3nix9EvalState17parseExprFromFileERKSs], [:],