s390: Enable s390 build in Makefile

Reviewed-by: Alice Frosi <alice@linux.vnet.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Reviewed-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

Makefile

@@ -21,7 +21,7 @@ UNAME-M := $(shell uname -m)
 
 #
 # Supported Architectures
-ifneq ($(filter-out x86 arm aarch64 ppc64,$(ARCH)),)
+ifneq ($(filter-out x86 arm aarch64 ppc64 s390,$(ARCH)),)
         $(error "The architecture $(ARCH) isn't supported")
 endif
 
@@ -65,6 +65,13 @@ ifeq ($(ARCH),x86)
         DEFINES		:= -DCONFIG_X86_64
 endif
 
+ifeq ($(ARCH),s390)
+        ARCH		:= s390
+        SRCARCH		:= s390
+        VDSO		:= y
+        DEFINES		:= -DCONFIG_S390
+endif
+
 LDARCH ?= $(SRCARCH)
 export LDARCH VDSO
 export PROTOUFIX DEFINES