Transmitted Alpine Linux flag makefile switch to C++ code

Change-Id: I1a5ba40f790f92cdc6430fbbad93b10ed6a60bca
Signed-off-by: Botond Baranyi <botond.baranyi@ericsson.com>

Makefile.cfg

@@ -369,6 +369,10 @@ ifeq ($(PLATFORM), LINUX)
     CPPFLAGS += -DUSE_EPOLL
 endif
 
+ifdef ALPINE_LINUX
+    CPPFLAGS += -DALPINE_LINUX
+endif
+
 #not useful in compiler2/asn1, for example
 #REL_DIR := $(notdir $(CURDIR))