gh-149833: Change DLL prefix to "cygpython" on Cygwin (#149834)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: carlo-bramini

configure

@@ -1591,7 +1591,7 @@ if test $enable_shared = "yes"; then
     CYGWIN*)
       LDLIBRARY='libpython$(LDVERSION).dll.a'
       BLDLIBRARY='-L. -lpython$(LDVERSION)'
-      DLLLIBRARY='libpython$(LDVERSION).dll'
+      DLLLIBRARY='cygpython$(LDVERSION).dll'
       ;;
     SunOS*)
       LDLIBRARY='libpython$(LDVERSION).so'