librhash: Disable warnings to avoid changing 3rd party code

Add '-w' or equivalent flag on compilers supporting it.
Tell MSVC to use its lowest warning level inside librhash sources.

Utilities/cmlibrhash/CMakeLists.txt

@@ -1,5 +1,13 @@
 project(librhash C)
 
+# Disable warnings to avoid changing 3rd party code.
+if(CMAKE_C_COMPILER_ID MATCHES
+    "^(GNU|Clang|AppleClang|XL|VisualAge|SunPro|MIPSpro|HP|Intel)$")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -w")
+elseif(CMAKE_C_COMPILER_ID STREQUAL "PathScale")
+  set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -woffall")
+endif()
+
 set(librhash_sources
   librhash/algorithms.c
   librhash/algorithms.h

Utilities/cmlibrhash/librhash/ustd.h

@@ -5,6 +5,10 @@
 /* Include KWSys Large File Support configuration. */
 #include <cmsys/Configure.h>
 
+#if defined(_MSC_VER)
+# pragma warning(push,1)
+#endif
+
 #if _MSC_VER >= 1300
 
 # define int64_t __int64