GH-438 Remove 'extern "C"' wrapper around Perl XS includes.

'extern "C" {}' block has wrapped Perl XS standard includes since the
beginning.  The earliest version found from the net is Net_SSLeay.pm version
0.4 in which the following was already present:

  #ifdef __cplusplus
  extern "C" {
  #endif
  #include "EXTERN.h"
  #include "perl.h"
  #include "XSUB.h"
  #ifdef __cplusplus
  }
  #endif

This has been carried over since then, until the recent SSLeay.xs updates to
allow compilation with a C++ compiler caused a compilation failure.

Recent GCC and Clang C++ compilers do not care about the 'extern "C"' wrapper
but Visual Studio Community 2022 flagged the following error (see GH-438):

C:\Program Files (x86)\Windows Kits\10\include\10.0.19041.0\um\wspiapi.h(53):
error C2894: templates cannot be declared to have 'C ' linkage

When 'extern "C" {}' is removed completely, the compilation succeeds. This
makes sense since apparently the purpose of 'extern "C" {}' is to wrap one's
own functions instead of headers included from elsewhere. Those headers should
have their own 'extern "C" {}' definitions, if any are needed.

2 files changed, 5 insertions, 6 deletions

diff --git a/Changes b/Changes
index 5245ed2..0aa47ea 100644
--- a/Changes
+++ b/Changes
@@ -89,6 +89,11 @@ Revision history for Perl extension Net::SSLeay.
 	- Add OpenSSL 3.2 and LibreSSL 3.8 minor releases to GitHub CI
 	  testing. Update existing OpenSSL releases to 1.1.1w, 3.0.12
 	  and 3.1.4.
+	- Support compiling SSLeay.xs with a C++ compiler. Thanks to
+	  James E Keenan and GitHub user twata1 for suggesting this,
+	  testing and providing detailed test reports. Tested with GCC
+	  13 g++, Clang 17 clang++ and Visual Studio Community 2022
+	  C++ compilers. Discussion in GH-425 and GH-438.
 
 1.93_02 2023-02-22
 	- Update ppport.h to version 3.68. This eliminates thousands of
diff --git a/SSLeay.xs b/SSLeay.xs
index df96ecb..f76960b 100644
--- a/SSLeay.xs
+++ b/SSLeay.xs
@@ -143,18 +143,12 @@
 #pragma clang diagnostic warning "-Wunknown-warning-option"
 #endif
 
-#ifdef __cplusplus
-extern "C" {
-#endif
 #include "EXTERN.h"
 #include "perl.h"
 #include "XSUB.h"
 #include <stdarg.h>
 #define NEED_my_snprintf
 #include "ppport.h"
-#ifdef __cplusplus
-}
-#endif
 
 /* Sigh: openssl 1.0 has
  typedef void *BLOCK;