Merge dashpay#918: Clean up configuration in gen_context

0706796 add ECMULT_GEN_PREC_BITS to basic_config.h (Aaron Voisine)
a3aa262 gen_context: Don't include basic-config.h (Tim Ruffing)

Pull request description:

ACKs for top commit:
  sipa:
    utACK 0706796
  jonasnick:
    ACK 0706796

Tree-SHA512: 4889b483a33ac54f6038a5a5db1ccd225b03e752c5724243db7345389372ecf043433fd5441199043fc8b74c963f13cbf6a7c8068367f9a105e2be93392f24e9

src/basic-config.h

@@ -9,16 +9,8 @@
 
 #ifdef USE_BASIC_CONFIG
 
-#undef USE_ASM_X86_64
-#undef USE_ECMULT_STATIC_PRECOMPUTATION
-#undef USE_EXTERNAL_ASM
-#undef USE_EXTERNAL_DEFAULT_CALLBACKS
-#undef USE_FORCE_WIDEMUL_INT64
-#undef USE_FORCE_WIDEMUL_INT128
-#undef ECMULT_WINDOW_SIZE
-
-#define USE_WIDEMUL_64 1
 #define ECMULT_WINDOW_SIZE 15
+#define ECMULT_GEN_PREC_BITS 4
 
 #endif /* USE_BASIC_CONFIG */
 

src/gen_context.c

@@ -9,8 +9,9 @@
 #if !defined(ECMULT_GEN_PREC_BITS)
 #include "libsecp256k1-config.h"
 #endif
-#define USE_BASIC_CONFIG 1
-#include "basic-config.h"
+
+/* We can't require the precomputed tables when creating them. */
+#undef USE_ECMULT_STATIC_PRECOMPUTATION
 
 #include "include/secp256k1.h"
 #include "assumptions.h"