cmake: Check compiler features

Github-Pull: #6
Rebased-From: 4cd5efd

cmake/bitcoin-config.h.in

@@ -6,6 +6,9 @@
 
 #define BITCOIN_CONFIG_H
 
+/* Define this symbol if type char equals int8_t */
+#cmakedefine CHAR_EQUALS_INT8 1
+
 /* Version Build */
 #define CLIENT_VERSION_BUILD @PROJECT_VERSION_PATCH@
 
@@ -119,6 +122,12 @@
    */
 #cmakedefine01 HAVE_DECL_SETSID
 
+/* Define if the visibility attribute is supported. */
+#cmakedefine HAVE_DEFAULT_VISIBILITY_ATTRIBUTE 1
+
+/* Define if the dllexport attribute is supported. */
+#cmakedefine HAVE_DLLEXPORT_ATTRIBUTE 1
+
 /* Define to 1 if you have the <endian.h> header file. */
 #cmakedefine HAVE_ENDIAN_H 1
 

cmake/introspection.cmake

@@ -240,3 +240,26 @@ check_cxx_source_compiles("
   }
   " HAVE_SYSCTL_ARND
 )
+
+check_cxx_source_compiles("
+  #include <cstdint>
+  #include <type_traits>
+
+  int main()
+  {
+    static_assert(std::is_same<int8_t, char>::value);
+  }
+  " CHAR_EQUALS_INT8
+)
+
+check_cxx_source_compiles("
+  int foo(void) __attribute__((visibility(\"default\")));
+  int main(){}
+  " HAVE_DEFAULT_VISIBILITY_ATTRIBUTE
+)
+
+check_cxx_source_compiles("
+  __declspec(dllexport) int foo(void);
+  int main(){}
+  " HAVE_DLLEXPORT_ATTRIBUTE
+)