[COFF] Don't round alignment if it's already a power-of-two

[davide]

Summary

This seems to match what link.exe does.

[ruiu]

LGTM with using PowerOf2Ceil.

COFF/Chunks.cpp

 void SectionChunk::replace(SectionChunk *Other) {
   Other->Repl = Repl;
   Other->Live = false;
 }
 
 CommonChunk::CommonChunk(const COFFSymbolRef S) : Sym(S) {
   // Common symbols are aligned on natural boundaries up to 32 bytes.
   // This is what MSVC link.exe does.
-  Align = std::min(uint64_t(32), NextPowerOf2(Sym.getValue()));
+  uint32_t Value = Sym.getValue();
+  Align = std::min(uint64_t(32),
+    isPowerOf2_64(Value) ? Value : NextPowerOf2(Value));
 }
 
 uint32_t CommonChunk::getPermissions() const {
   return IMAGE_SCN_CNT_UNINITIALIZED_DATA | IMAGE_SCN_MEM_READ |
          IMAGE_SCN_MEM_WRITE;
 }
 
 void StringChunk::writeTo(uint8_t *Buf) const {

test/COFF/common.test

 # RUN: yaml2obj %s > %t.obj
 # RUN: lld-link /out:%t.exe /entry:main %t.obj %t.obj
 # RUN: llvm-objdump -d %t.exe | FileCheck %s
 
 # Operands of B8 (MOV EAX) are common symbols
 # CHECK: 3000: b8 00 10 00 40
 # CHECK: 3005: b8 04 10 00 40
 # CHECK: 300a: b8 20 10 00 40
 # CHECK: 300f: b8 60 10 00 40
-# CHECK: 3014: b8 80 10 00 40
+# CHECK: 3014: b8 70 10 00 40
 
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_AMD64
   Characteristics: []
 sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]