vty: Add a file for C++ functions

Currently the pcu_vty.c doesn't compile with C++. Thus C++ object
cannot be access directly there.

This commit adds a helper C++ file that exports all functions with C
calling conventions and naming to work around that limitation until
the transition of pcu_vty.c is completed.

Sponsored-by: On-Waves ehf
diff --git a/src/Makefile.am b/src/Makefile.am
index 35ba7a9..b18c1ce 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -43,6 +43,7 @@
 	bitvector.cpp \
 	pcu_l1_if.cpp \
 	pcu_vty.c \
+	pcu_vty_functions.cpp \
 	tbf.cpp \
 	tbf_ul.cpp \
 	tbf_dl.cpp \
@@ -85,6 +86,7 @@
 	gsm_timer.h \
 	bitvector.h \
 	pcu_vty.h \
+	pcu_vty_functions.h \
 	sysmo_l1_if.h \
 	femtobts.h \
 	tbf.h \