Fix prefixed names on MSVC.

MSVC does not define __USER_LABEL_PREFIX__, however on all such
platforms it is entirely correct to define it to be empty.

Bug: 42220000
Change-Id: Ic28e58faeb6532e89838181756f4d0ec6a6a6964
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/90387
Reviewed-by: Xiangfei Ding <xfding@google.com>
Commit-Queue: Xiangfei Ding <xfding@google.com>

include/openssl/prefix_symbols.h

diff --git a/include/openssl/prefix_symbols.h b/include/openssl/prefix_symbols.h
index 200aad0..c58129e 100644
--- a/include/openssl/prefix_symbols.h
+++ b/include/openssl/prefix_symbols.h
@@ -22,10 +22,16 @@
 
 #if defined(BORINGSSL_PREFIX)
 
+#if defined(__USER_LABEL_PREFIX__)
+#define BORINGSSL_USER_LABEL_PREFIX __USER_LABEL_PREFIX__
+#else
+#define BORINGSSL_USER_LABEL_PREFIX
+#endif
+
 #define BORINGSSL_CONCAT_INNER(a, b) a##b
 #define BORINGSSL_CONCAT(a, b) BORINGSSL_CONCAT_INNER(a, b)
 #define BORINGSSL_ADD_PREFIX(s) BORINGSSL_CONCAT(BORINGSSL_PREFIX, BORINGSSL_CONCAT(_, s))
-#define BORINGSSL_ADD_USER_LABEL_AND_PREFIX(s) BORINGSSL_CONCAT(BORINGSSL_CONCAT(__USER_LABEL_PREFIX__, BORINGSSL_PREFIX), BORINGSSL_CONCAT(_, s))
+#define BORINGSSL_ADD_USER_LABEL_AND_PREFIX(s) BORINGSSL_CONCAT(BORINGSSL_CONCAT(BORINGSSL_USER_LABEL_PREFIX, BORINGSSL_PREFIX), BORINGSSL_CONCAT(_, s))
 
 #if defined(__PRAGMA_REDEFINE_EXTNAME) && !defined(__ASSEMBLER__)
 

util/pregenerate/idextractor.go

diff --git a/util/pregenerate/idextractor.go b/util/pregenerate/idextractor.go
index 3f9b5fd..f511da0 100644
--- a/util/pregenerate/idextractor.go
+++ b/util/pregenerate/idextractor.go
@@ -209,10 +209,16 @@
 
 #if defined(BORINGSSL_PREFIX)
 
+#if defined(__USER_LABEL_PREFIX__)
+#define BORINGSSL_USER_LABEL_PREFIX __USER_LABEL_PREFIX__
+#else
+#define BORINGSSL_USER_LABEL_PREFIX
+#endif
+
 #define BORINGSSL_CONCAT_INNER(a, b) a##b
 #define BORINGSSL_CONCAT(a, b) BORINGSSL_CONCAT_INNER(a, b)
 #define BORINGSSL_ADD_PREFIX(s) BORINGSSL_CONCAT(BORINGSSL_PREFIX, BORINGSSL_CONCAT(_, s))
-#define BORINGSSL_ADD_USER_LABEL_AND_PREFIX(s) BORINGSSL_CONCAT(BORINGSSL_CONCAT(__USER_LABEL_PREFIX__, BORINGSSL_PREFIX), BORINGSSL_CONCAT(_, s))
+#define BORINGSSL_ADD_USER_LABEL_AND_PREFIX(s) BORINGSSL_CONCAT(BORINGSSL_CONCAT(BORINGSSL_USER_LABEL_PREFIX, BORINGSSL_PREFIX), BORINGSSL_CONCAT(_, s))
 
 `)
 	output.WriteString("#if defined(__PRAGMA_REDEFINE_EXTNAME) && !defined(__ASSEMBLER__)\n")