Draft: Revert "configure: quiet a warning" because it breaks crosscompiling.

From the commit message I couldn't see what warning was silenced and how important the subdir-objects parameter is in order to build correctly. I don't want to step on the author's toes with this revert, it's rather a base for discussion (hence marked as draft).

Actually I think I might face an autotools bug. Using the subdir-objects parameter makes autotools create a folder $(srcdir)/.deps in the wrong destination, which leads to the assumption that the autotools codegeneration bugs when used in an crosscompiling environment.