fix(windows): resolve P256 ADX assembly linking error on MinGW (#139)

Author: lparam

btls-sys/build/main.rs

@@ -477,6 +477,9 @@ fn ensure_patches_applied(config: &Config) -> io::Result<()> {
     println!("cargo:warning=applying loongarch patch to boringssl");
     apply_patch(config, "boringssl-loongarch.patch")?;
 
+    println!("cargo:warning=applying windows cross compile patch to boringssl");
+    apply_patch(config, "boringssl-windows.patch")?;
+
     if config.features.underscore_wildcards {
         println!("cargo:warning=applying underscore wildcards patch to boringssl");
         apply_patch(config, "underscore-wildcards.patch")?;

btls-sys/patches/boringssl-windows.patch

@@ -0,0 +1,29 @@
+--- a/third_party/fiat/p256_64.h
++++ b/third_party/fiat/p256_64.h
+@@ -3,7 +3,7 @@
+ #include "p256_field_64.br.c.inc"
+ #include "../../crypto/internal.h"
+ 
+-#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) && defined(__x86_64__)
++#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) && defined(__x86_64__) && !defined(__MINGW32__)
+ extern "C" {
+ void fiat_p256_adx_mul(uint64_t*, const uint64_t*, const uint64_t*);
+ void fiat_p256_adx_sqr(uint64_t*, const uint64_t*);
+@@ -181,7 +181,7 @@
+  */
+ static FIAT_P256_FIAT_INLINE void fiat_p256_mul(fiat_p256_montgomery_domain_field_element out1, const fiat_p256_montgomery_domain_field_element arg1, const fiat_p256_montgomery_domain_field_element arg2) {
+   // NOTE: edited by hand, see third_party/fiat/README.md
+-#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) && defined(__x86_64__)
++#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) && defined(__x86_64__) && !defined(__MINGW32__)
+   if (CRYPTO_is_BMI1_capable() && CRYPTO_is_BMI2_capable() &&
+     CRYPTO_is_ADX_capable()) {
+       fiat_p256_adx_mul(out1, arg1, arg2);
+@@ -497,7 +497,7 @@
+  */
+ static FIAT_P256_FIAT_INLINE void fiat_p256_square(fiat_p256_montgomery_domain_field_element out1, const fiat_p256_montgomery_domain_field_element arg1) {
+   // NOTE: edited by hand, see third_party/fiat/README.md
+-#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) && defined(__x86_64__)
++#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) && defined(__x86_64__) && !defined(__MINGW32__)
+   if (CRYPTO_is_BMI1_capable() && CRYPTO_is_BMI2_capable() &&
+     CRYPTO_is_ADX_capable()) {
+       fiat_p256_adx_sqr(out1, arg1);