Skip t0204 for MinGW Git

As per https://msdn.microsoft.com/en-us/library/x99tb11d.aspx:

	The set of available locale names, languages, country/region
	codes, and code pages includes all those supported by the Windows
	NLS API except code pages that require more than two bytes per
	character, such as UTF-7 and UTF-8.

Therefore, MinGW gettext cannot cope with UTF-8 at all, because it uses
the Win32 API internally.

However, when the test asks `locale -a` it reports that is_US.utf8 is
available, because that `locale` is actually an *MSys2* program (and MSys2
can cope with UTF-8 alright).

Let's just skip this test for MinGW Git altogether.

Helped-by: 마누엘 <nalla@users.noreply.github.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

t/t0204-gettext-reencode-sanity.sh

@@ -7,6 +7,15 @@ test_description="Gettext reencoding of our *.po/*.mo files works"
 
 . ./lib-gettext.sh
 
+if test_have_prereq MINGW
+then
+	# There is no MinGW 'locale', but an MSys2 one that interferes
+	# with this test (the MinGW and MSys2 locales are in fundamentally
+	# different realms).
+	skip_all='No native locale.exe available'
+	test_done
+fi
+
 # The constants used in a tricky observation for undefined behaviour
 RUNES="TILRAUN: ᚻᛖ ᚳᚹᚫᚦ ᚦᚫᛏ ᚻᛖ ᛒᚢᛞᛖ ᚩᚾ ᚦᚫᛗ ᛚᚪᚾᛞᛖ ᚾᚩᚱᚦᚹᛖᚪᚱᛞᚢᛗ ᚹᛁᚦ ᚦᚪ ᚹᛖᛥᚫ"
 PUNTS="TILRAUN: ?? ???? ??? ?? ???? ?? ??? ????? ??????????? ??? ?? ????"