include: fix prereq tests for perl and file (#18911)

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@44296 3c298f89-4303-0410-b956-a3cf2f4a3e73

include/prereq-build.mk

@@ -132,7 +132,7 @@ $(eval $(call SetupHostCommand,wget,Please install GNU 'wget', \
 	wget --version | grep GNU))
 
 $(eval $(call SetupHostCommand,perl,Please install Perl 5.x, \
-	perl --version | grep "perl 5"))
+	perl --version | grep "perl.*v5"))
 
 $(eval $(call SetupHostCommand,python,Please install Python 2.x, \
 	python2.7 -V 2>&1 | grep Python, \
@@ -146,7 +146,7 @@ $(eval $(call SetupHostCommand,git,Please install Git (git-core) >= 1.6.5, \
 	git clone 2>&1 | grep -- --recursive))
 
 $(eval $(call SetupHostCommand,file,Please install the 'file' package, \
-	file --version | grep file))
+	file --version 2>&1 | grep file))
 
 $(eval $(call SetupHostCommand,openssl,Please install the 'openssl' utility, \
 	openssl version | grep OpenSSL))