tpm2-tss: declare dependency on a toolchain with C++

Version 1.4.0 still contains some C++ code. This has already changed on
upstream, so future versions will drop the dependency on a C++ compiler.

[Peter: fix indentation, add dependency to config option]
Signed-off-by: Carlos Santos <casantos@datacom.ind.br>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/tpm2-tss/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_TPM2_TSS
 	bool "tpm2-tss"
+	depends on BR2_INSTALL_LIBSTDCPP
 	select BR2_PACKAGE_LIBURIPARSER
 	help
 	  OSS implementation of the Trusted Computing Group's (TCG) TPM2
@@ -29,3 +30,6 @@ config BR2_PACKAGE_TPM2_TSS
 	    Microsoft software TPM2 simulator.
 
 	  https://github.com/tpm2-software/tpm2-tss
+
+comment "tpm2-tss needs a toolchain w/ C++"
+	depends on !BR2_INSTALL_LIBSTDCPP