[lld/mac] Inline a check

[thakis]

Summary

match() can only return for non-empty vectors, but at least in
non-LTO builds that isn't clear to the compiler. Help it out.
This is a minor but measurable speedup on my machine (but less
than what we might've lost in https://reviews.llvm.org/D100818#2764272 --
bot note higher N on this measurement here, so higher confidence here):

% ministat at_main at_branch
x at_main
+ at_branch
    N           Min           Max        Median           Avg        Stddev
x  30     3.9243979     4.0395119      3.987375     3.9826236   0.027567796
+  30     3.8495831     4.0009291      3.931325     3.9347135   0.037832878
Difference at 95.0% confidence
        -0.0479101 +/- 0.0171102
        -1.20298% +/- 0.429622%
        (Student's t, pooled s = 0.0331007)

No behavior change.

Eventually we should apply these lists at symbol parse time instead of
every time shouldExportSymbol() though :)

[int3]

nice!

lld/MachO/SyntheticSections.cpp

static bool shouldExportSymbol(const Defined *defined) {
   // global symbols in the input but uses -exported_symbols to filter
   // out most of them, then it would be better to set the value of
   // privateExtern at parse time instead of calling
   // exportedSymbols.match() more than once.
   //
   // Measurements show that symbol ordering (which again looks up
   // every symbol in a hashmap) is the biggest bottleneck when linking
   // chromium_framework, so this will likely be worth optimizing.
-  return config->exportedSymbols.empty()
-             ? !config->unexportedSymbols.match(defined->getName())
-             : config->exportedSymbols.match(defined->getName());
+  if (!config->exportedSymbols.empty())
+    return config->exportedSymbols.match(defined->getName());
+  if (!config->unexportedSymbols.empty())
+    return !config->unexportedSymbols.match(defined->getName());
+  return true;
 }
 
 void ExportSection::finalizeContents() {
   trieBuilder.setImageBase(in.header->addr);
   for (const Symbol *sym : symtab->getSymbols()) {
     if (const auto *defined = dyn_cast<Defined>(sym)) {
       validateExportSymbol(defined);
       if (!shouldExportSymbol(defined))