Re-enable global suppression of MSVC warnings.

There are hundreds of these, and most of them appear to be in the unit tests, not the actual Thrust headers.
It's turning into a rabbit hole and dragging beyond the scope of the current PR.
Filed NVIDIA#2409 to track the removal of these suppressions.

Author: alliepiper

thrust/cmake/ThrustBuildCompilerTargets.cmake

@@ -16,6 +16,13 @@ function(thrust_build_compiler_targets)
   set(cxx_compile_options)
   set(cxx_compile_definitions)
 
+  # Disabled loss-of-data conversion warnings.
+  # TODO Re-enable.
+  append_option_if_available("/wd4244" cxx_compile_options)
+
+  # Disable warning about applying unary operator- to unsigned type.
+  # TODO Re-enable.
+  append_option_if_available("/wd4146" cxx_compile_options)
 
   if (THRUST_DISPATCH_TYPE STREQUAL "Force32bit")
     list(APPEND cxx_compile_definitions "THRUST_FORCE_32_BIT_OFFSET_TYPE")