[lldb] Add omitted abstract formal parameters in DWARF symbol files

This patch fixes a problem introduced by clang change
https://reviews.llvm.org/D95617 and described by
https://bugs.llvm.org/show_bug.cgi?id=50076#c6, where inlined functions
omit unused parameters both in the stack trace and in `frame var`
command. With this patch, the parameters are listed correctly in the
stack trace and in `frame var` command.

Specifically, we parse formal parameters from the abstract version of
inlined functions and use those formal parameters if they are missing
from the concrete version.

Differential Revision: https://reviews.llvm.org/D110571

lldb/test/API/functionalities/unused-inlined-parameters/Makefile

@@ -0,0 +1,4 @@
+C_SOURCES := main.c
+CFLAGS_EXTRAS := -O1
+
+include Makefile.rules

lldb/test/API/functionalities/unused-inlined-parameters/TestUnusedInlinedParameters.py

@@ -0,0 +1,22 @@
+"""
+Test that unused inlined parameters are displayed.
+"""
+
+import lldb
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class TestUnusedInlinedParameters(TestBase):
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test_unused_inlined_parameters(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.c"))
+
+        # For the unused parameters, only check the types.
+        self.assertIn("(void *) unused1 = <no location, value may have been optimized out>",
+                      lldbutil.get_description(self.frame().FindVariable("unused1")))
+        self.assertEqual(42, self.frame().FindVariable("used").GetValueAsUnsigned())
+        self.assertIn("(int) unused2 = <no location, value may have been optimized out>",
+                      lldbutil.get_description(self.frame().FindVariable("unused2")))

lldb/test/API/functionalities/unused-inlined-parameters/main.c

@@ -0,0 +1,12 @@
+#include <stdio.h>
+
+__attribute__((optnone)) __attribute__((nodebug)) void use(int used) {}
+
+__attribute__((always_inline)) void f(void *unused1, int used, int unused2) {
+  use(used); // break here
+}
+
+int main(int argc, char **argv) {
+  f(argv, 42, 1);
+  return 0;
+}