[lld-macho]][nfc] Fix some typos + rephrase a comment

[int3]

Summary

I was a bit confused by the comment because I thought that "Tests
that..." was describing the tests contained within the same file.

[thakis]

Seems small enough to qualify for post-commit review :) But lg anyways, thanks!

lld/MachO/SyntheticSections.cpp

switch (config->outputType) {
     // (rather than 0). But we need to do that after assignAddresses().
   case MH_EXECUTE:
     // If linking PIE, __mh_execute_header is a defined symbol in
     //  __TEXT, __text)
     // Otherwise, it's an absolute symbol.
     if (config->isPic)
       symtab->addSynthetic("__mh_execute_header", in.header->isec, 0,
                            /*privateExtern=*/false,
-                           /*includeInSymbtab=*/true);
+                           /*includeInSymtab=*/true);
     else
       symtab->addSynthetic("__mh_execute_header",
                            /*isec*/ nullptr, 0,
                            /*privateExtern=*/false,
-                           /*includeInSymbtab=*/true);
+                           /*includeInSymtab=*/true);
     break;
 
     // The following symbols are  N_SECT symbols, even though the header is not
     // part of any section and that they are private to the bundle/dylib/object
     // they are part of.
   case MH_BUNDLE:
     addHeaderSymbol("__mh_bundle_header");
     break;

lld/test/MachO/private-extern.s

 # EXPORTS-DAG:   [[#%x, BAR_ADDR:]] g {{.*}} _bar
 # EXPORTS-LABEL: Exports trie:
 # EXPORTS-NOT:   0x{{0*}}[[#%X, FOO_ADDR]] _foo
 # EXPORTS-DAG:   0x{{0*}}[[#%X, BAR_ADDR]] _bar
 # EXPORTS-NOT:   0x{{0*}}[[#%X, FOO_ADDR]] _foo
 # EXPORTS-NM-DAG: (__TEXT,__cstring) non-external (was a private external) _foo
 # EXPORTS-NM-DAG: (__TEXT,__cstring) external _bar
 
-# Tests that weak private_exten symbols aren't referenced in the
-# weak bind table are in weak-private.extern.s
+## The tests for weak .private_extern symbols not being referenced in the
+## weak bind table can be found in weak-private-extern.s
 
 #--- basics.s
 .section __TEXT,__cstring
 
 .globl _foo, _bar
 .private_extern _foo
 
 _foo: