message: configure: keep relative paths in debug info
  Revert to the state prior to and allow debugging
  from project root dir with `gdb src/bitcoind`.
diff: @@ -1672,8 +1672,8 @@ if test "x$use_ccache" != "xno"; then
  fi
  AC_MSG_RESULT($use_ccache)
  if test "x$use_ccache" = "xyes"; then
  - AX_CHECK_COMPILE_FLAG([-fdebug-prefix-map=A=B],[DEBUG_CXXFLAGS="$DEBUG_CXXFLAGS -fdebug-prefix-map=\$(abs_srcdir)=."],,[[$CXXFLAG_WERROR]])
  - AX_CHECK_PREPROC_FLAG([-fmacro-prefix-map=A=B],[DEBUG_CPPFLAGS="$DEBUG_CPPFLAGS -fmacro-prefix-map=\$(abs_srcdir)=."],,[[$CXXFLAG_WERROR]])
  + AX_CHECK_COMPILE_FLAG([-fdebug-prefix-map=A=B],[DEBUG_CXXFLAGS="$DEBUG_CXXFLAGS -fdebug-prefix-map=\$(abs_top_srcdir)=."],,[[$CXXFLAG_WERROR]])
  + AX_CHECK_PREPROC_FLAG([-fmacro-prefix-map=A=B],[DEBUG_CPPFLAGS="$DEBUG_CPPFLAGS -fmacro-prefix-map=\$(abs_top_srcdir)=."],,[[$CXXFLAG_WERROR]])
  fi
  fi
  