Add 'remark' diagnostic type in LLVM

A 'remark' is information that is not an error or a warning, but rather some
additional information provided to the user. In contrast to a 'note' a 'remark'
is an independent diagnostic, whereas a 'note' always depends on another
diagnostic.

A typical use case for remark nodes is information provided to the user, e.g.
information provided by the vectorizer about loops that have been vectorized.

llvm-svn: 202474
diff --git a/llvm/include/llvm-c/lto.h b/llvm/include/llvm-c/lto.h
index bff63ad..87904c2 100644
--- a/llvm/include/llvm-c/lto.h
+++ b/llvm/include/llvm-c/lto.h
@@ -40,7 +40,7 @@
  * @{
  */
 
-#define LTO_API_VERSION 9
+#define LTO_API_VERSION 10
 
 /**
  * \since prior to LTO_API_VERSION=3
@@ -299,9 +299,10 @@
  * \since LTO_API_VERSION=7
  */
 typedef enum {
-  LTO_DS_ERROR,
-  LTO_DS_WARNING,
-  LTO_DS_NOTE
+  LTO_DS_ERROR = 0,
+  LTO_DS_WARNING = 1,
+  LTO_DS_REMARK = 3, // Added in LTO_API_VERSION=10.
+  LTO_DS_NOTE = 2
 } lto_codegen_diagnostic_severity_t;
 
 /**