[libclang] Use strict prototypes in header

[aaronpuchert]

Summary

When included in a C program, these function declarations are treated as
K&R declarations, which conveys no information about the number of
arguments of the function. A function with no arguments has to be
declared with parameter-type-list "void".

[aaronpuchert]

Can be "reproduced" with clang -fsyntax-only -Wstrict-prototypes clang/include/clang-c/*.h.

[aaronpuchert]

Fixed by @aaron.ballman in rC373213 along with another issue.

clang/include/clang-c/FatalErrorHandler.h

 #ifdef __cplusplus
 extern "C" {
 #endif
 
 /**
  * Installs error handler that prints error message to stderr and calls abort().
  * Replaces currently installed error handler (if any).
  */
-void clang_install_aborting_llvm_fatal_error_handler();
+void clang_install_aborting_llvm_fatal_error_handler(void);
 
 /**
  * Removes currently installed error handler (if any).
  * If no error handler is intalled, the default strategy is to print error
  * message to stderr and call exit(1).
  */
-void clang_uninstall_llvm_fatal_error_handler();
+void clang_uninstall_llvm_fatal_error_handler(void);
 
 #ifdef __cplusplus
 }
 #endif
 #endif