Description:
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At the moment, during the configure stage at compile time, it is determined which shared memory variants are available. For this, tiny C programms are just-in-time compiled and then defines are set.

This does not work well when cross-compiling as we do for OpenWrt for example: we could try to successfully compile the programm, but it is not possible to actually run it.
So without further modification this leads to a php binary/opcache addon which does not have _any_ shared memory implementation compiled in, and it results in errors like this one:
https://github.com/openwrt/packages/issues/1010

Maybe it possible to not rely the detection on such run-during-compile tests? I'm no autoconf expert, but I wonder whether there is a possibility to "preseed" the test results?
To make it work for OpenWrt, we hacked a patch which simply checks for one important function used by one SHM implementation or the other. But this might not be sufficient.