I did a fresh update of Cygwin and then downloaded the 21.1.14 tarball. Configure was run without any options. It failed to find XPM because the first of the two test programs would not compile because X11 header files could not be found. Configure for 21.2.43 does correctly detect XPM. I don't understand configure well enough to create a patch, but the only difference in the XPM section of the two configure scripts is that the 21.2.43 version has the line "#define XPM_NUMBERS" at line 7543 of the file. This would be at line 6958 of the 21.1.14 version.