Fix msys library name in import libraries

Cygwin's speclib doesn't handle dashes or dots. However, we are about to
rename the output file name from `cygwin1.dll` to `msys-2.0.dll`.

Let's preemptively fix up all the import libraries that would link
against `msys_2_0.dll` to correctly link against `msys-2.0.dll` instead.

Author: ktbarrett

winsup/cygwin/scripts/speclib

@@ -38,6 +38,7 @@ while (<$nm_fd>) {
     study;
     if (/ I _?(.*)_dll_iname/o) {
 	$dllname = $1;
+	$dllname =~ s/_2_0/-2.0/;
     } else {
 	my ($file, $member, $symbol) = m%^([^:]*):([^:]*(?=:))?.* T (.*)%o;
 	next if !defined($symbol) || $symbol =~ $exclude_regex;