Replace Gnulib's "getopt" module with "getopt-gnu"

The "getopt" module is marked as deprecated, these days we're supposed
to choose either "getopt-posix" or "getopt-gnu".

gl/Makefile.am

@@ -21,7 +21,7 @@
 # the same distribution terms as the rest of that program.
 #
 # Generated by gnulib-tool.
-# Reproduce by: gnulib-tool --import --dir=. --lib=libgnu --source-base=gl --m4-base=gl/m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --no-conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files base64 crypto/sha1 dirname environ floorf fsusage getaddrinfo gethostname getloadavg getopt gettext mountlist regex setenv strsep timegm unsetenv vasprintf vsnprintf
+# Reproduce by: gnulib-tool --import --dir=. --lib=libgnu --source-base=gl --m4-base=gl/m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --no-conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files base64 crypto/sha1 dirname environ floorf fsusage getaddrinfo gethostname getloadavg getopt-gnu gettext mountlist regex setenv strsep timegm unsetenv vasprintf vsnprintf
 
 AUTOMAKE_OPTIONS = 1.9.6 gnits subdir-objects
 

gl/m4/gnulib-cache.m4

@@ -27,7 +27,7 @@
 
 
 # Specification in the form of a command-line invocation:
-#   gnulib-tool --import --dir=. --lib=libgnu --source-base=gl --m4-base=gl/m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --no-conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files base64 crypto/sha1 dirname environ floorf fsusage getaddrinfo gethostname getloadavg getopt gettext mountlist regex setenv strsep timegm unsetenv vasprintf vsnprintf
+#   gnulib-tool --import --dir=. --lib=libgnu --source-base=gl --m4-base=gl/m4 --doc-base=doc --tests-base=tests --aux-dir=build-aux --no-conditional-dependencies --no-libtool --macro-prefix=gl --no-vc-files base64 crypto/sha1 dirname environ floorf fsusage getaddrinfo gethostname getloadavg getopt-gnu gettext mountlist regex setenv strsep timegm unsetenv vasprintf vsnprintf
 
 # Specification in the form of a few gnulib-tool.m4 macro invocations:
 gl_LOCAL_DIR([])
@@ -41,7 +41,7 @@ gl_MODULES([
   getaddrinfo
   gethostname
   getloadavg
-  getopt
+  getopt-gnu
   gettext
   mountlist
   regex

gl/m4/gnulib-comp.m4

@@ -64,7 +64,6 @@ AC_DEFUN([gl_EARLY],
   # Code from module getaddrinfo:
   # Code from module gethostname:
   # Code from module getloadavg:
-  # Code from module getopt:
   # Code from module getopt-gnu:
   # Code from module getopt-posix:
   # Code from module gettext: