sr/srd/cli: Fix compiling with Homebrew.

Add ACLOCAL_DIR setting and AM_PROG_AR macro for compiling with Homebrew
under Mac OS X.

Applies essentially the same change to
{libsigrok,libsigrokdecode,sigrok-cli}/{autogen.sh,configure.ac}

It may be that the same fix is needed for the other autogen.sh and/or
configure.ac files, but that hasn't been tested and therefore not in
this commit.
diff --git a/autogen.sh b/autogen.sh
index a49d17b..8185af0 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -32,6 +32,9 @@
 	elif [ -d /opt/local/share/aclocal ]; then
 		# Macports installs aclocal macros here
 		ACLOCAL_DIR="-I /opt/local/share/aclocal"
+	elif [ -d /usr/local/share/aclocal ]; then
+		# Homebrew installs aclocal macros here
+		ACLOCAL_DIR="-I /usr/local/share/aclocal"
 	elif [ -d /usr/share/aclocal ]; then
 		# Xcode installs aclocal macros here
 		ACLOCAL_DIR="-I /usr/share/aclocal"