This change has an impact on downstream packagers and users of Python 3.8 because the SOABI flag values are also used to construct a number of file names and directories names in an Unix or macOS framework install besides the extension module (*.so) file names.  Suggest comparing the directory/file names installed to an alternate prefix (./configure --prefix=/tmp/3x ; make install) in 3.7 versus master with this PR.  Also suggest reading PEP 3149, which introduced the ABI-specific file names, and the various issues in the bug tracker that reference it.  At the very least, these changes need to be documented in the What's New for 3.8.  But the impact of the change should probably also be discussed with at least some of the large distributors.  (The change already inadvertently broke the macOS installer build - fixing.)