[Driver] Add aliases for -Qn/-Qy

[miyuki]

Summary

This patch adds aliases for -Qn (-fno-ident) and -Qy (-fident) which
look less cryptic than -Qn/-Qy. The aliases are compatible with GCC.

CodeGen/no-ident-version.c

 // RUN: %clang_cc1 -emit-llvm -debug-info-kind=limited -o - %s \
 // RUN:   | FileCheck --check-prefix=CHECK-NONE %s
 // RUN: %clang_cc1 -Qn -emit-llvm -debug-info-kind=limited -o - %s \
 // RUN:   | FileCheck --check-prefix=CHECK-QN %s
+// RUN: %clang_cc1 -fno-ident -emit-llvm -debug-info-kind=limited -o - %s \
+// RUN:   | FileCheck --check-prefix=CHECK-QN %s
 // RUN: %clang_cc1 -Qy -emit-llvm -debug-info-kind=limited -o - %s \
 // RUN:   | FileCheck --check-prefix=CHECK-QY %s
+// RUN: %clang_cc1 -fident -emit-llvm -debug-info-kind=limited -o - %s \
+// RUN:   | FileCheck --check-prefix=CHECK-QY %s
 
 // CHECK-NONE: @main
 // CHECK-NONE: llvm.ident
 // CHECK-NONE: producer:
 
 // CHECK-QN: @main
 // CHECK-QN-NOT: llvm.ident
 // CHECK-QN-NOT: producer:
 
 // CHECK-QY: @main
 // CHECK-QY: llvm.ident
 // CHECK-QY: producer:
 int main(void) {}

clang/Driver/Options.td

 def O_flag : Flag<["-"], "O">, Flags<[CC1Option]>, Alias<O>, AliasArgs<["2"]>;
 def Ofast : Joined<["-"], "Ofast">, Group<O_Group>, Flags<[CC1Option]>;
 def P : Flag<["-"], "P">, Flags<[CC1Option]>, Group<Preprocessor_Group>,
   HelpText<"Disable linemarker output in -E mode">;
 def Qy : Flag<["-"], "Qy">, Flags<[CC1Option]>,
   HelpText<"Emit metadata containing compiler name and version">;
 def Qn : Flag<["-"], "Qn">, Flags<[CC1Option]>,
   HelpText<"Do not emit metadata containing compiler name and version">;
+def : Flag<["-"], "fident">, Group<f_Group>, Alias<Qy>, Flags<[CC1Option]>;
+def : Flag<["-"], "fno-ident">, Group<f_Group>, Alias<Qn>, Flags<[CC1Option]>;
 def Qunused_arguments : Flag<["-"], "Qunused-arguments">, Flags<[DriverOption, CoreOption]>,
   HelpText<"Don't emit warning for unused driver arguments">;
 def Q : Flag<["-"], "Q">, IgnoredGCCCompat;
 def Rpass_EQ : Joined<["-"], "Rpass=">, Group<R_value_Group>, Flags<[CC1Option]>,
   HelpText<"Report transformations performed by optimization passes whose "
            "name matches the given POSIX regular expression">;
 def Rpass_missed_EQ : Joined<["-"], "Rpass-missed=">, Group<R_value_Group>,
   Flags<[CC1Option]>,

 defm float_store : BooleanFFlag<"float-store">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm friend_injection : BooleanFFlag<"friend-injection">, Group<clang_ignored_f_Group>;
 defm function_attribute_list : BooleanFFlag<"function-attribute-list">, Group<clang_ignored_f_Group>;
 defm gcse : BooleanFFlag<"gcse">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm gcse_after_reload: BooleanFFlag<"gcse-after-reload">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm gcse_las: BooleanFFlag<"gcse-las">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm gcse_sm: BooleanFFlag<"gcse-sm">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm gnu : BooleanFFlag<"gnu">, Group<clang_ignored_f_Group>;
-defm ident : BooleanFFlag<"ident">, Group<clang_ignored_f_Group>;
 defm implicit_templates : BooleanFFlag<"implicit-templates">, Group<clang_ignored_f_Group>;
 defm implement_inlines : BooleanFFlag<"implement-inlines">, Group<clang_ignored_f_Group>;
 defm merge_constants : BooleanFFlag<"merge-constants">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm modulo_sched : BooleanFFlag<"modulo-sched">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm modulo_sched_allow_regmoves : BooleanFFlag<"modulo-sched-allow-regmoves">,
     Group<clang_ignored_gcc_optimization_f_Group>;
 defm inline_functions_called_once : BooleanFFlag<"inline-functions-called-once">,
     Group<clang_ignored_gcc_optimization_f_Group>;