[Frontend][PCH]-Add support for ignoring PCH options (-ignore-pch). (#142409)

Visual Studio has an argument to ignore all PCH related switches. clang-cl has also support option /Y-. Having the same option in clang would be helpful. This commit is to add support for ignoring PCH options (-ignore-pch).

The commit includes:
    1. Implement -ignore-pch as a Driver option.
    2. Add a Driver test and a PCH test.
    3. Add a section of -ignore-pch to user manual.
    4. Add a release note for the new option '-ignore-pch'.

Code reviewed by: Matheus Izvekov <mizvekov@gmail.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index 80728da..a03fd50 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -4331,6 +4331,15 @@ void Driver::handleArguments(Compilation &C, DerivedArgList &Args,
     YcArg = YuArg = nullptr;
   }
 
+  if (Args.hasArg(options::OPT_include_pch) &&
+      (FinalPhase == phases::Preprocess ||
+       Args.hasArg(options::OPT_ignore_pch))) {
+    // If only preprocessing or -ignore-pch is used, -include-pch is disabled.
+    // Since -emit-pch is CC1option, it will not be added to command argments if
+    // -ignore-pch is used.
+    Args.eraseArg(options::OPT_include_pch);
+  }
+
   bool LinkOnly = phases::Link == FinalPhase && Inputs.size() > 0;
   for (auto &I : Inputs) {
     types::ID InputType = I.first;