Support LibreSSL as provider of openssl

The build scripts check for openssl by grepping the string "OpenSSL" in
the output of openssl version command. LibreSSL fails this test as it
outputs something like "LibreSSL 2.2.4". This patch fix the
prereq-bulid.mk file so that it accepts LibreSSL as openssl provider as
well.

Signed-off-by: Marek Behun <kabel@blackhole.sk>

SVN-Revision: 48267

include/prereq-build.mk

@@ -161,7 +161,7 @@ $(eval $(call SetupHostCommand,file,Please install the 'file' package, \
 	file --version 2>&1 | grep file))
 
 $(eval $(call SetupHostCommand,openssl,Please install the 'openssl' utility, \
-	openssl version | grep OpenSSL))
+	openssl version | grep '\(OpenSSL\|LibreSSL\)'))
 
 
 # Install ldconfig stub