[3.14] gh-140041: Fix import of `ctypes` on Android and Cygwin when ABI flags are present (GH-140178) (#140180)

Use sysconfig to determine the full name of libpython, rather than hardcoding
a library name that doesn't have ABI flags.
(cherry picked from commit 7f371ed84ba471bb1b11e79b502f244a9c17ac84)

Co-authored-by: Malcolm Smith <smith@chaquo.com>