Fix gnutls error code check; don't autoupdate for brew install (#772) #1209

Job	Run time
check-ubuntu-openssl111	1m 10s
check-ubuntu-openssl111 (--enable-static-linking=yes --without-nss --without-gcrypt --without-gnu...	1m 8s
check-osx	12m 34s
check-mingw (MINGW64, x86_64, --enable-unicode=yes)	18m 18s
check-msvc (mscng, unicode=yes with-dl=yes)	2m 31s
check-mingw (MINGW64, x86_64, --enable-static --enable-static-linking --enable-unicode=no --enabl...	11m 21s
check-ubuntu-openssl300	3m 24s
check-msvc (mscng, unicode=no with-dl=no static=yes legacy-crypto=yes)	2m 53s
check-ubuntu-openssl300 (--enable-static --enable-static-linking --without-nss --without-gcrypt -...	1m 16s
check-ubuntu-openssl300 (--enable-static --enable-static-linking --enable-ftp --enable-md5 --enab...	1m 0s
check-msvc (mscrypto, unicode=yes with-dl=yes)	2m 14s
check-msvc (mscrypto, unicode=no with-dl=no static=yes legacy-crypto=yes)	2m 14s
check-msvc (openssl-300, unicode=yes with-dl=yes)	7m 12s
check-msvc (openssl-300, unicode=no with-dl=no static=yes)	6m 16s
	1h 13m 31s

Provide feedback