build: require secp256k1 be built first in Makefile

-this clears up an issue where when running make libsecp256k1.la was missing when libtool required it

Makefile.am

@@ -10,6 +10,17 @@ LIBSECP256K1=src/secp256k1/libsecp256k1.la
 $(LIBSECP256K1): $(wildcard src/secp256k1/src/*) $(wildcard src/secp256k1/include/*)
 	$(AM_V_at)$(MAKE) $(AM_MAKEFLAGS) -C $(@D) $(@F)
 
+SUBDIRS = $(DIST_SUBDIRS)
+
+.PHONY: subdirs $(SUBDIRS)
+
+subdirs: $(SUBDIRS)
+
+$(SUBDIRS):
+		$(MAKE) -C $@
+
+libdogecoin: src/secp256k1
+
 includedir = $(prefix)/include/dogecoin
 
 lib_LTLIBRARIES = libdogecoin.la
@@ -264,6 +275,3 @@ endif
 endif
 
 libdogecoin_la_LDFLAGS = -no-undefined -version-info $(LIB_VERSION_CURRENT):$(LIB_VERSION_REVISION):$(LIB_VERSION_AGE)
-
-clean-local:
-	-$(MAKE) -C src/secp256k1 clean