Problem: curve keygen build cannot be switched off

Makefile.am

@@ -282,10 +282,12 @@ perf_inproc_thr_LDADD = src/libzmq.la
 perf_inproc_thr_SOURCES = perf/inproc_thr.cpp
 endif
 
+if ENABLE_CURVE_KEYGEN
 bin_PROGRAMS = tools/curve_keygen
 
 tools_curve_keygen_LDADD = src/libzmq.la
 tools_curve_keygen_SOURCES = tools/curve_keygen.cpp
+endif
 
 #
 # tests

configure.ac

@@ -354,6 +354,14 @@ AC_ARG_ENABLE([perf],
 
 AM_CONDITIONAL(ENABLE_PERF, test "x$zmq_enable_perf" = "xyes")
 
+# Conditionally build curve key generation tool
+AC_ARG_ENABLE([curve-keygen],
+    [AS_HELP_STRING([--enable-curve-keygen], [Build curve key-generation tool [default=yes].])],
+    [zmq_enable_curve_keygen=$enableval],
+    [zmq_enable_curve_keygen=yes])
+
+AM_CONDITIONAL(ENABLE_CURVE_KEYGEN, test "x$zmq_enable_curve_keygen" = "xyes")
+
 # Use c++ in subsequent tests
 AC_LANG_PUSH(C++)