Add missing `extern` qualifiers for gcc 10

GCC 10 defaults to `-fno-common`. no longer automatically sharing
global variable definitions, which makes it important to define
them in only one place (otherwise there will be duplicate definition
errors). Add `extern` qualifiers where (I think) is the best place for
them.

common/daemon.c

@@ -18,8 +18,6 @@
 #include <unistd.h>
 #include <wally_core.h>
 
-struct backtrace_state *backtrace_state;
-
 #if BACKTRACE_SUPPORTED
 static void (*bt_print)(const char *fmt, ...) PRINTF_FMT(1,2);
 static void (*bt_exit)(void);

common/daemon.h

@@ -20,6 +20,4 @@ void daemon_shutdown(void);
 /* Kick in a debugger if they set --debugger */
 void daemon_maybe_debug(char *argv[]);
 
-struct backtrace_state *backtrace_state;
-
 #endif /* LIGHTNING_COMMON_DAEMON_H */

common/memleak.c

@@ -7,6 +7,8 @@
 #include <common/memleak.h>
 #include <common/utils.h>
 
+struct backtrace_state *backtrace_state;
+
 #if DEVELOPER
 static bool memleak_track;
 

common/memleak.h

@@ -66,4 +66,6 @@ void memleak_scan_region(struct htable *memtable,
 /* Get (and remove) a leak from memtable, or NULL */
 const void *memleak_get(struct htable *memtable, const uintptr_t **backtrace);
 
+extern struct backtrace_state *backtrace_state;
+
 #endif /* LIGHTNING_COMMON_MEMLEAK_H */

common/test/run-sphinx.c

@@ -47,7 +47,7 @@ size_t bigsize_put(u8 buf[BIGSIZE_MAX_LEN] UNNEEDED, bigsize_t v UNNEEDED)
 { fprintf(stderr, "bigsize_put called!\n"); abort(); }
 /* AUTOGENERATED MOCKS END */
 
-secp256k1_context *secp256k1_ctx;
+extern secp256k1_context *secp256k1_ctx;
 
 static struct secret secret_from_hex(const char *hex)
 {

connectd/test/run-initiator-success.c

@@ -104,7 +104,7 @@ static bool secret_eq_str(const struct secret *s, const char *str)
 	return secret_eq_consttime(s, &expect);
 }
 
-secp256k1_context *secp256k1_ctx;
+extern secp256k1_context *secp256k1_ctx;
 const void *trc;
 static struct pubkey rs_pub, ls_pub, e_pub;
 static struct privkey ls_priv, e_priv;

connectd/test/run-responder-success.c

@@ -104,7 +104,7 @@ static bool secret_eq_str(const struct secret *s, const char *str)
 	return secret_eq_consttime(s, &expect);
 }
 
-secp256k1_context *secp256k1_ctx;
+extern secp256k1_context *secp256k1_ctx;
 static struct pubkey ls_pub, e_pub;
 static struct privkey ls_priv, e_priv;
 

plugins/libplugin.c

@@ -35,7 +35,7 @@ static size_t in_timer;
 
 bool deprecated_apis;
 
-const struct chainparams *chainparams;
+extern const struct chainparams *chainparams;
 
 struct plugin_timer {
 	struct timer timer;

wire/test/run-peer-wire.c

@@ -12,7 +12,7 @@
 #include <common/sphinx.h>
 #include <wire/gen_peer_wire.h>
 
-secp256k1_context *secp256k1_ctx;
+extern secp256k1_context *secp256k1_ctx;
 
 /* AUTOGENERATED MOCKS START */
 /* Generated stub for amount_asset_is_main */