Use extern "C" for sha1

src/sha1.h

@@ -25,17 +25,21 @@
  * none of the original Mozilla code remains.
  */
 
-typedef struct {
-    unsigned long long size;
-    unsigned int H[5];
-    unsigned int W[16];
-} blk_SHA_CTX;
+extern "C" {
 
-void blk_SHA1_Init(blk_SHA_CTX *ctx);
-void blk_SHA1_Update(blk_SHA_CTX *ctx, const void *dataIn, unsigned long len);
-void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *ctx);
+    typedef struct {
+        unsigned long long size;
+        unsigned int H[5];
+        unsigned int W[16];
+    } blk_SHA_CTX;
+
+    void blk_SHA1_Init(blk_SHA_CTX *ctx);
+    void blk_SHA1_Update(blk_SHA_CTX *ctx, const void *dataIn, unsigned long len);
+    void blk_SHA1_Final(unsigned char hashout[20], blk_SHA_CTX *ctx);
 
 #define git_SHA_CTX	blk_SHA_CTX
 #define git_SHA1_Init	blk_SHA1_Init
 #define git_SHA1_Update	blk_SHA1_Update
 #define git_SHA1_Final	blk_SHA1_Final
+
+}