ccmake: Fix compilation with ncurses on Solaris

On Solaris the ncurses header may define an `__attribute__` macro.
This breaks C++ headers that use `__attribute__(...)` syntax.
Somehow it causes references to unresolved symbols:

    __gthrw_pthread_once
    __gthrw_pthread_mutex_lock
    __gthrw_pthread_mutex_unlock

instead of references to the correct symbols:

    pthread_once
    pthread_mutex_lock
    pthread_mutex_unlock

Detect this case and undefine the `__attribute__` macro after
including the curses headers.

Source/CursesDialog/cmCursesStandardIncludes.h

@@ -5,6 +5,11 @@
 
 #include "cmConfigure.h" // IWYU pragma: keep
 
+// Record whether __attribute__ is currently defined.  See purpose below.
+#ifndef __attribute__
+#define cm_no__attribute__
+#endif
+
 #if defined(__hpux)
 #define _BOOL_DEFINED
 #include <sys/time.h>
@@ -29,4 +34,12 @@ inline void curses_clear()
 #undef erase
 #undef clear
 
+// The curses headers on some platforms (e.g. Solaris) may
+// define __attribute__ as a macro.  This breaks C++ headers
+// in some cases, so undefine it now.
+#if defined(cm_no__attribute__) && defined(__attribute__)
+#undef __attribute__
+#endif
+#undef cm_no__attribute__
+
 #endif // cmCursesStandardIncludes_h