Index: PCbuild/build_ssl.py
===================================================================
--- PCbuild/build_ssl.py	(revision 84924)
+++ PCbuild/build_ssl.py	(working copy)
@@ -148,6 +148,23 @@
     print(do_script)
     os.system(do_script)
 
+def copy(src, dst):
+    """Copies file src to dst
+
+    But file won't be copied when contents of two files are same
+    """
+    if os.path.isfile(dst):
+        bufsize = 1024 * 8
+        with open(src, "rb") as src_f, open(dst, "rb") as dst_f:
+            while True:
+                src_s = src_f.read(bufsize)
+                dst_s = dst_f.read(bufsize)
+                if src_s != dst_s:
+                    break
+                if not src_s:
+                    return
+    shutil.copy(src, dst)
+
 def main():
     build_all = "-a" in sys.argv
     if sys.argv[1] == "Release":
@@ -224,15 +241,16 @@
             if arch == "amd64":
                 create_makefile64(makefile, m32)
             fix_makefile(makefile)
-            shutil.copy2(r"crypto\buildinf.h", r"crypto\buildinf_%s.h" % arch)
-            shutil.copy2(r"crypto\opensslconf.h", r"crypto\opensslconf_%s.h" % arch)
+            copy(r"crypto\buildinf.h", r"crypto\buildinf_%s.h" % arch)
+            copy(r"crypto\opensslconf.h", r"crypto\opensslconf_%s.h" % arch)
 
         # If the assembler files don't exist in tmpXX, copy them there
         if not os.path.exists("tmp"+dirsuffix):
             os.mkdir("tmp"+dirsuffix)
         for f in os.listdir("asm"+dirsuffix):
             if not f.endswith(".asm"): continue
-            shutil.copy2(r"asm%s\%s" % (dirsuffix, f), "tmp"+dirsuffix)
+            if os.path.isfile(r"tmp%s\%s" % (dirsuffix, f)): continue
+            shutil.copy(r"asm%s\%s" % (dirsuffix, f), "tmp"+dirsuffix)
 
         # Now run make.
         if arch == "amd64":
@@ -241,8 +259,8 @@
                 print("ml64 assembler has failed.")
                 sys.exit(rc)
 
-        shutil.copy2(r"crypto\buildinf_%s.h" % arch, r"crypto\buildinf.h")
-        shutil.copy2(r"crypto\opensslconf_%s.h" % arch, r"crypto\opensslconf.h")
+        copy(r"crypto\buildinf_%s.h" % arch, r"crypto\buildinf.h")
+        copy(r"crypto\opensslconf_%s.h" % arch, r"crypto\opensslconf.h")
 
         #makeCommand = "nmake /nologo PERL=\"%s\" -f \"%s\"" %(perl, makefile)
         makeCommand = "nmake /nologo -f \"%s\"" % makefile