[pdbutil] Add a command to dump the FPM.

Recently problems have been discovered in the way we write the FPM
(free page map).  In order to fix this, we first need to establish
a baseline about what a correct FPM looks like using an MSVC
generated PDB, so that we can then make our own generated PDBs
match.  And in order to do this, the dumper needs a mode where it
can dump an FPM so that we can write tests for it.

This patch adds a command to dump the FPM, as well as a test against
a known-good PDB.

llvm-svn: 309894
diff --git a/llvm/lib/DebugInfo/MSF/MSFCommon.cpp b/llvm/lib/DebugInfo/MSF/MSFCommon.cpp
index 1facf5e..484e184 100644
--- a/llvm/lib/DebugInfo/MSF/MSFCommon.cpp
+++ b/llvm/lib/DebugInfo/MSF/MSFCommon.cpp
@@ -59,3 +59,18 @@
 
   return Error::success();
 }
+
+MSFStreamLayout llvm::msf::getFpmStreamLayout(const MSFLayout &Msf) {
+  MSFStreamLayout FL;
+  uint32_t NumFpmIntervals = getNumFpmIntervals(Msf);
+  support::ulittle32_t FpmBlock = Msf.SB->FreeBlockMapBlock;
+  assert(FpmBlock == 1 || FpmBlock == 2);
+  while (NumFpmIntervals > 0) {
+    FL.Blocks.push_back(FpmBlock);
+    FpmBlock += msf::getFpmIntervalLength(Msf);
+    --NumFpmIntervals;
+  }
+  FL.Length = getFullFpmByteSize(Msf);
+
+  return FL;
+}