config: add $egrep

Introduce a new variable set in $PLAN9/config:
$egrep, which is conditionally set to either
`egrep` or `grep -E`, based on platform, and use
this when we want to invoke `egrep`.

This works around the endless warnings from GNU
grep stating that `egrep` is deprecated in favor
of `grep -E`, when run on e.g. Linux.

bin/9c

@@ -8,6 +8,7 @@ usegcc()
 		-O2 \
 		-c \
 		-Wall \
+		-Wno-array-parameter \
 		-Wno-parentheses \
 		-Wno-missing-braces \
 		-Wno-switch \
@@ -23,7 +24,7 @@ usegcc()
 		-fno-omit-frame-pointer \
 		-fsigned-char \
 		-fcommon \
-		-std=c11 \
+		-std=gnu11 \
 	"
 	# want to put -fno-optimize-sibling-calls here but
 	# that option only works with gcc3+ it seems
@@ -56,7 +57,7 @@ quiet()
 	ignore=$ignore'|expanded from macro'
 
 	grep -v '__p9l_autolib_' "$1" |
-	egrep -v "$ignore" |
+	$egrep -v "$ignore" |
 	sed 's/ .first use in this function.$//; s/\"\([^\"][^\"]*\)\", line \([0-9][0-9]*\)/\1:\2/g' |
 	$(which uniq) 1>&2  # avoid built-in uniq on SunOS
 }

bin/9l

@@ -146,7 +146,7 @@ then
 					grep '__p9l_autolib_[a-zA-Z0-9+-]*' |
 					sed 's/.*__p9l_autolib_//; s/:.*//' |
 					sort -u |
-					egrep -v '^(thread|draw)$'
+					$egrep -v '^(thread|draw)$'
 				`
 				a="$a $b"
 			done
@@ -337,7 +337,7 @@ quiet()
 	ignore=$ignore'|ld: warning: ignoring duplicate libraries:'
 
 	sed 's/.*: In function `[^:]*: *//' "$1" |
-	egrep -v "$ignore"
+	$egrep -v "$ignore"
 }
 
 # Must use temp file to avoid pipe; pipe loses status.