field_gmp's negate doesn't need to use the magnitude argument.

Makefile.am

@@ -37,7 +37,8 @@ noinst_HEADERS += src/field_5x52_int128_impl.h
 noinst_HEADERS += src/field_5x52_asm_impl.h
 noinst_HEADERS += src/java/org_bitcoin_NativeSecp256k1.h
 noinst_HEADERS += src/util.h
-noinst_HEADERS += src/util_impl.h
+noinst_HEADERS += src/testrand.h
+noinst_HEADERS += src/testrand_impl.h
 noinst_HEADERS += src/field_gmp.h
 noinst_HEADERS += src/field_gmp_impl.h
 noinst_HEADERS += src/field.h

src/field_gmp_impl.h

@@ -97,6 +97,7 @@ static void secp256k1_fe_get_b32(unsigned char *r, const secp256k1_fe_t *a) {
 }
 
 SECP256K1_INLINE static void secp256k1_fe_negate(secp256k1_fe_t *r, const secp256k1_fe_t *a, int m) {
+    (void)m;
     *r = *a;
     secp256k1_fe_normalize(r);
     for (int i=0; i<FIELD_LIMBS; i++)