[llvm] [BOLT] Add --pad-funcs-before=func:n (PR #117924)

[Maksim Panchenko via llvm-commits]

================
@@ -319,6 +349,36 @@ bool BinaryEmitter::emitFunction(BinaryFunction &Function,
     Streamer.emitCodeAlignment(Function.getAlign(), &*BC.STI);
   }
 
+  if (size_t Padding = opts::padFunctionBefore(Function)) {
+    // Handle padFuncsBefore after the above alignment logic but before
+    // symbol addresses are decided; with the intent that the nops are
+    // not executed and the original alignment logic is preserved.
+    if (!BC.HasRelocations) {
+      errs() << "BOLT-ERROR: -pad-before-funcs is not supported in "
+             << "non-relocation mode\n";
+      exit(1);
+    }
+
+    // Preserve Function.getMinAlign().
+    if (!isAligned(Function.getMinAlign(), Padding)) {
+      errs() << "BOLT-ERROR: User-requested " << Padding
----------------
maksfb wrote:

nit:
```
BC.errs() << "BOLT-ERROR: user-requested " << Padding

https://github.com/llvm/llvm-project/pull/117924