Fix known typos

Sweep the codebase for common typos. Includes some changes to visible function
names that were misspelt.

llvm-svn: 200018
diff --git a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
index c5d9612..1c8f928 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -7205,7 +7205,7 @@
       // you might suspect (sizeof(vector) bytes after the last requested
       // load), but rather sizeof(vector) - 1 bytes after the last
       // requested vector. The point of this is to avoid a page fault if the
-      // base address happend to be aligned. This works because if the base
+      // base address happened to be aligned. This works because if the base
       // address is aligned, then adding less than a full vector length will
       // cause the last vector in the sequence to be (re)loaded. Otherwise,
       // the next vector will be fetched as you might suspect was necessary.