csprng: fixed to build if the libc is not including an internal argp implementation

security/csprng/csprng.conf

@@ -24,3 +24,10 @@ if atstage cross; then
 	# and our stage 0 compile only supports C
 	var_append extraconfopt ' ' "--disable-http-rng"
 fi
+
+# if the standalone argp implementation is used because the libc used
+# is not including argp support, like musl or uClibc we need to tell
+# the linker about it.
+if pkginstalled argp-standalone; then
+	var_append configprefix ' ' "LDFLAGS=-largp"
+fi