Regeneration of the platdir files needs to be aware of the value of sysroot [1]. For example on Android cross-builds, sysroot must be set to the path of the headers and libraries for the targeted Android API level corresponding to a version of the Android libc and a version of Android. So, automatically regenerating those files in this case requires to look into the CC, CFLAGS and CPPFLAGS environment variables for sysroot. OTOH RTLD_* constants are exposed in the posix module (issue 13226) and the platdir files usefulness is limited now.

Cross building from one linux architecture to another is possible with gnu make VPATH support by building outside the source tree. Android is also a linux architecture and building outside the source tree makes sense, not only to work around the problem described in the second item of msg241143, but also to build for different Android API levels and identify the results of those builds.

It is not clear that the changes made in this issue fixes correctly issue 22724, see msg269359.

I think the scope of this isssue should be restricted to multiarch build systems, i.e. when gcc has been configured with '--enable-multiarch' [2].

[1] Options for Directory Search: https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html
[2] Installing GCC: Configuration: https://gcc.gnu.org/install/configure.html