[lldb/testsuite] Fix TestInlineStepping on arm64 with newer compilers

Summary:
TestInlineStepping tests LLDB's ability to step in the presence of
inline frames. The testcase source has a number of functions and some
of them are marked `always_inline`.

The test is built around the assumption that the inline function will
be fully represented once inlined, but this is not true with the
current arm64 code generation. For example:

void caller() {
     always_inline_function(); // Step here
}

When stppeing into `caller()` above, you might immediatly end up in
the inlines frame for `always_inline_function()`, because there might
literally be no code associated with `caller()` itself.

This patch hacks around the issue by adding an `asm volatile("nop")`
on some lines with inlined calls where we expect to be able to
step. Like so:

void caller() {
     asm volatile("nop"); always_inline_function(); // Step here
}

This guarantees there is always going to be one instruction for this
line in the caller.

Reviewers: labath, jingham

Subscribers: kristof.beyls, danielkiss, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D76406

Author: fredriss

lldb/test/API/functionalities/inline-stepping/calling.cpp

@@ -75,7 +75,7 @@ caller_trivial_1 ()
 void
 caller_trivial_2 ()
 {
-    inline_trivial_1 (); // In caller_trivial_2.
+    asm volatile ("nop"); inline_trivial_1 (); // In caller_trivial_2.
     inline_value += 1;  // At increment in caller_trivial_2.
 }
 
@@ -88,7 +88,7 @@ called_by_inline_trivial ()
 void
 inline_trivial_1 ()
 {
-    inline_trivial_2(); // In inline_trivial_1.
+    asm volatile ("nop"); inline_trivial_2(); // In inline_trivial_1.
     inline_value += 1;  // At increment in inline_trivial_1.
 }