package/fluidsynth: needs C++

fluidsynth needs C++ since bump to version 2.2.0 in commit
7e02d2e762eb94fde1f222df1b960dbd263fa946 and
https://github.com/FluidSynth/fluidsynth/commit/0d98c47545aa2424741c0cc2b244e4f73249302c:

CMake Error at CMakeLists.txt:32 (project):
  No CMAKE_CXX_COMPILER could be found.

Fixes:
 - http://autobuild.buildroot.org/results/fe677f7b38c8ed7011f1c976bdb45768067936f7

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/fluidsynth/Config.in

@@ -6,6 +6,7 @@ config BR2_PACKAGE_FLUIDSYNTH
 	# the .pc file installed by fluidsynth does not mention its
 	# indirect dependencies in Libs.private.
 	depends on !BR2_STATIC_LIBS
+	depends on BR2_INSTALL_LIBSTDCPP
 	select BR2_PACKAGE_LIBGLIB2
 	help
 	  FluidSynth is a real-time software synthesizer based on the
@@ -128,7 +129,7 @@ config BR2_PACKAGE_FLUIDSYNTH_READLINE
 
 endif # BR2_PACKAGE_FLUIDSYNTH
 
-comment "fluidsynth needs a toolchain w/ threads, wchar, dynamic library"
+comment "fluidsynth needs a toolchain w/ threads, wchar, dynamic library, C++"
 	depends on BR2_USE_MMU
 	depends on !BR2_USE_WCHAR || !BR2_TOOLCHAIN_HAS_THREADS || \
-		BR2_STATIC_LIBS
+		BR2_STATIC_LIBS || !BR2_INSTALL_LIBSTDCPP