Merge c9f0a78432 into f2539bbe34

Unlike on Windows, it is perfectly acceptable to set symbol visibility
for static libraries, and it magically works. In fact, it even
beneficially does something useful.

This simplifies the code by avoiding special cases.

include/mimalloc.h

@@ -60,11 +60,7 @@ terms of the MIT license. A copy of the license can be found in the file
   #define mi_attr_alloc_size2(s1,s2)
   #define mi_attr_alloc_align(p)
 #elif defined(__GNUC__)                 // includes clang and icc
-  #if defined(MI_SHARED_LIB) && defined(MI_SHARED_LIB_EXPORT)
-    #define mi_decl_export              __attribute__((visibility("default")))
-  #else
-    #define mi_decl_export
-  #endif
+  #define mi_decl_export              __attribute__((visibility("default")))
   #define mi_cdecl                      // leads to warnings... __attribute__((cdecl))
   #define mi_decl_restrict
   #define mi_attr_malloc                __attribute__((malloc))