bpo-35550: Fix incorrect Solaris define guards (GH-11275)


Python source code uses on several places ifdef sun or defined(sun) without the underscores, which is not standard compliant and shouldn't be used.

Defines should check for __sun instead. Reference: http://nadeausoftware.com/articles/2012/01/c_c_tip_how_use_compiler_predefined_macros_detect_operating_systemGH-Solaris

https://bugs.python.org/issue35550
(cherry picked from commit 6f9bc72c79c3262e5d0f2c0e96b016477399cfb1)

Co-authored-by: Jakub KulĂ­k <Kulikjak@gmail.com>
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 661e1bd..988471e 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -265,7 +265,7 @@
 #endif
 
 /* Solaris fails to define this variable at all. */
-#if defined(sun) && !defined(INET_ADDRSTRLEN)
+#if (defined(__sun) && defined(__SVR4)) && !defined(INET_ADDRSTRLEN)
 #define INET_ADDRSTRLEN 16
 #endif