build: adapt Windows builds for libsecp256k1 build changes

See bitcoin-core/secp256k1#1367.

(cherry picked from commit bitcoin/bitcoin@5080c9c)

Zcash: Without changes to `build_msvc/` as we removed it.

Author: fanquake

configure.ac

@@ -573,6 +573,8 @@ case $host in
 
      ZC_REQUIRE_TOOL(WINDRES, windres)
 
+     CORE_CPPFLAGS="$CORE_CPPFLAGS -DSECP256K1_STATIC"
+
      CPPFLAGS="$CPPFLAGS -D_MT -DWIN32 -D_WINDOWS -DBOOST_THREAD_USE_LIB -D_WIN32_WINNT=0x0601 -D_WIN32_IE=0x0501 -DWIN32_LEAN_AND_MEAN"
 
      dnl libtool insists upon adding -nostdlib and a list of objects/libs to link against.