build: add gettext[tools] vcpkg dep

Add gettext vcpkg dependency lib with the [tools] feature for the msgfmt
utility to build the translations.

Can be disabled by setting the NO_GETTEXT environment variable, support
for which was added in 2cd6269 (build: support NO_LIB env to disable
vcpkg deps, 2022-03-17).

Signed-off-by: Rafael Kitover <[email protected]>

compat/vcbuild/vcpkg_install.bat

@@ -72,7 +72,7 @@ REM ================================================================
 :install_libraries
 
 	echo Installing third-party libraries(%arch%), this may take a while...
-	FOR %%i IN (zlib expat libiconv openssl libssh2 curl) DO (
+	FOR %%i IN (zlib expat libiconv openssl libssh2 curl gettext) DO (
 	    IF NOT DEFINED NO_%%i (
 		cd %VCPKG_ROOT%
 		IF NOT EXIST "packages\%%i_%arch%" CALL :sub__install_one %%i
@@ -140,3 +140,7 @@ goto :EOF
 :curl_features
 set features=[core,openssl,schannel]
 goto :EOF
+
+:gettext_features
+set features=[tools]
+goto :EOF