AC_FUNC_MALLOC & AC_FUNC_REALLOC cause link errors when cross-compiling.
It seems the preferred solution is to just remove them, and optionally adding
them to the AC_CHECK_FUNCS section.
Examples:
- https://github.com/LLNL/ior/issues/4
- https://github.com/stakizawa/kmrnext/commit/47331724c1b1010b4adcad936f6aa14bde1ddebb
- https://github.com/eribertomota/axel/commit/6667e4cb91ef3f5ac25cea02e3cd5ea49d48b3e3
(used as template for this commit message; thanks!)
- https://rickfoosusa.blogspot.de/2011/11/howto-fix-undefined-reference-to.html