boost: graph needs regex

output/host/usr/bin/m68k-linux-readelf -d output/staging/usr/lib/libboost_graph.so

Dynamic section at offset 0x47f00 contains 28 entries:
  Tag        Type                         Name/Value
 0x00000001 (NEEDED)                     Shared library: [libboost_regex.so.1.67.0]

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/boost/Config.in

@@ -156,6 +156,7 @@ config BR2_PACKAGE_BOOST_FILESYSTEM
 
 config BR2_PACKAGE_BOOST_GRAPH
 	bool "boost-graph"
+	select BR2_PACKAGE_BOOST_REGEX
 	help
 	  The BGL graph interface and graph components are generic, in
 	  the same sense as the the Standard Template Library (STL).