Fix mingw64 linking bugs

Makefile.am

@@ -146,13 +146,19 @@ ecdsa_example_SOURCES = examples/ecdsa.c
 ecdsa_example_CPPFLAGS = -I$(top_srcdir)/include
 ecdsa_example_LDADD = libsecp256k1.la
 ecdsa_example_LDFLAGS = -static
+if BUILD_WINDOWS
+ecdsa_example_LDFLAGS += -lbcrypt
+endif
 TESTS += ecdsa_example
 if ENABLE_MODULE_ECDH
 noinst_PROGRAMS += ecdh_example
 ecdh_example_SOURCES = examples/ecdh.c
 ecdh_example_CPPFLAGS = -I$(top_srcdir)/include
 ecdh_example_LDADD = libsecp256k1.la
 ecdh_example_LDFLAGS = -static
+if BUILD_WINDOWS
+ecdh_example_LDFLAGS += -lbcrypt
+endif
 TESTS += ecdh_example
 endif
 if ENABLE_MODULE_SCHNORRSIG
@@ -161,6 +167,9 @@ schnorr_example_SOURCES = examples/schnorr.c
 schnorr_example_CPPFLAGS = -I$(top_srcdir)/include
 schnorr_example_LDADD = libsecp256k1.la
 schnorr_example_LDFLAGS = -static
+if BUILD_WINDOWS
+schnorr_example_LDFLAGS += -lbcrypt
+endif
 TESTS += schnorr_example
 endif
 endif

configure.ac

@@ -45,6 +45,8 @@ if test x"$ac_cv_prog_cc_c89" = x"no"; then
 fi
 AM_PROG_AS
 
+build_windows=no
+
 case $host_os in
   *darwin*)
      if  test x$cross_compiling != xyes; then
@@ -68,6 +70,9 @@ case $host_os in
        fi
      fi
    ;;
+   cygwin*|mingw*)
+     build_windows=yes
+   ;;
 esac
 
 # Try if some desirable compiler flags are supported and append them to SECP_CFLAGS.
@@ -406,6 +411,7 @@ AM_CONDITIONAL([ENABLE_MODULE_EXTRAKEYS], [test x"$enable_module_extrakeys" = x"
 AM_CONDITIONAL([ENABLE_MODULE_SCHNORRSIG], [test x"$enable_module_schnorrsig" = x"yes"])
 AM_CONDITIONAL([USE_EXTERNAL_ASM], [test x"$use_external_asm" = x"yes"])
 AM_CONDITIONAL([USE_ASM_ARM], [test x"$set_asm" = x"arm"])
+AM_CONDITIONAL([BUILD_WINDOWS], [test "$build_windows" = "yes"])
 AC_SUBST(LIB_VERSION_CURRENT, _LIB_VERSION_CURRENT)
 AC_SUBST(LIB_VERSION_REVISION, _LIB_VERSION_REVISION)
 AC_SUBST(LIB_VERSION_AGE, _LIB_VERSION_AGE)

examples/random.h

@@ -16,6 +16,8 @@
  */
 
 #if defined(_WIN32)
+#include <windows.h>
+#include <ntstatus.h>
 #include <bcrypt.h>
 #elif defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
 #include <sys/random.h>