makepkg-git: do include gettext and error_highlight

In msys2/MSYS2-packages@d7c37ffdadd, `gettext`
was identified as an incorrect dependency of the `xz` package and that
dependency was dropped.

As a consequence, Git for Windows no longer included `gettext`, which
uncovered a bug in the definition of the `makepkg-git` SDK artifact
where it relied on that implicit dependency instead of making it an
explicit requirement (because it is needed by `makepkg` and
`makepkg-mingw`).

Let's make it explicit that `gettext.exe` (and `xgettext.exe`) are to be
included in the `makepkg-git` SDK artifact.

While at it, also avoid the "`error_highlight' was not loaded." warning
when building Git for Windows' `mingw-w64-git-doc-html` package.

This addresses the previously-forgotten x86_64 part of
git-for-windows/git#4952; The i686 part of was
fixed by git-for-windows/build-extra#560
already.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

.sparse/makepkg-git

@@ -52,6 +52,14 @@
 /usr/share/makepkg/
 /usr/bin/zstd.exe
 
+# gettext (for makepkg)
+/usr/bin/gettext.exe
+/usr/bin/xgettext.exe
+/usr/bin/msys-gettext*.dll
+
+# The `error_highlight` Ruby gem, needed by `asciidoctor`
+*error_highlight*
+
 # AsciiDoctor
 /mingw64/bin/asciidoctor
 /mingw64/bin/ruby.exe