package/libgeos: depends on wchar

libgeos unconditionally uses wstring which raises the following build
failure:

In file included from /srv/storage/autobuild/run/instance-3/output-1/build/libgeos-3.9.0/tools/astyle/ASLocalizer.cpp:40:
/srv/storage/autobuild/run/instance-3/output-1/build/libgeos-3.9.0/tools/astyle/ASLocalizer.h:72:34: error: 'wstring' does not name a type; did you mean 'stdin'?
  string convertToMultiByte(const wstring& wideStr) const;
                                  ^~~~~~~
                                  stdin

Fixes:
 - http://autobuild.buildroot.org/results/e97d03848d9bbf1845b994f391679a1dbf49f61e

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

package/libgeos/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_LIBGEOS
 	bool "libgeos"
 	depends on BR2_INSTALL_LIBSTDCPP
+	depends on BR2_USE_WCHAR
 	help
 	  GEOS (Geometry Engine - Open Source) is a C++ port of the
 	  JTS Topology Suite (JTS). It aims to contain the complete
@@ -10,5 +11,5 @@ config BR2_PACKAGE_LIBGEOS
 
 	  https://trac.osgeo.org/geos
 
-comment "libgeos needs a toolchain w/ C++"
-	depends on !BR2_INSTALL_LIBSTDCPP
+comment "libgeos needs a toolchain w/ C++, wchar"
+	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_USE_WCHAR