libzds: add curl interface to access zosmf rest api

Add library functions that allow to communicate with z/OSMF REST services
using libcurl.
Following three functions are added:

lzds_rest_get_enq()
	to obtain an ENQ that will mark a dataset as in use to z/OS until
	it is released again
lzds_rest_release_enq()
	to release an ENQ and mark a dataset as no longer in use to z/OS
lzds_rest_ping()
	to ping a z/OSMF REST server to check if it accessible
	or to refresh an ENQ and prevent it from a timeout after 10 minutes

Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

dasdview/Makefile

@@ -1,14 +1,39 @@
 include ../common.mak
 
-ALL_CPPFLAGS += -DSYSFS
-
-all: dasdview
-
 libs =	$(rootdir)/libdasd/libdasd.a \
 	$(rootdir)/libzds/libzds.a \
 	$(rootdir)/libvtoc/libvtoc.a \
 	$(rootdir)/libutil/libutil.a
 
+ifneq (${HAVE_CURL},0)
+
+check_dep:
+	$(call check_dep, \
+		"dasdview", \
+		"curl/curl.h", \
+		"curl-devel or libcurl-dev", \
+		"HAVE_CURL=0")
+
+BUILDTARGET = check_dep
+
+ifneq ($(shell sh -c 'command -v pkg-config'),)
+CURL_CFLAGS = $(shell pkg-config --silence-errors --cflags libcurl)
+CURL_LDLIBS = $(shell pkg-config --silence-errors --libs libcurl)
+else
+CURL_CFLAGS = -I/usr/include/s390x-linux-gnu/curl
+CURL_LDLIBS = -lcurl
+endif # shell
+
+endif # HAVE_CURL
+
+BUILDTARGET += dasdview
+
+ALL_CPPFLAGS += -DSYSFS
+ALL_CFLAGS += $(CURL_CFLAGS)
+LDLIBS += $(CURL_LDLIBS)
+
+all: $(BUILDTARGET)
+
 dasdview: dasdview.o $(libs)
 
 install: all