Refactor basic/intmath tests into a single file (#757)

* Refactor basic/intmath tests into a single file

These six tests previously duplicated almost all of their sources in
separate files. Bring them into a single file with templated routines
to perform the tests.

This change also makes use of more C++ features and utilities from the
harness library to make the code cleaner.

* Fix array indices for initialization

* Use loop for buffer creation

* Refactor to remove duplicate verification code

Remove need for hardcoded number of test operations.

* Address review comments

* Use TEST_SKIPPED_ITSELF

test_conformance/basic/CMakeLists.txt

@@ -3,8 +3,7 @@ set(MODULE_NAME BASIC)
 set(${MODULE_NAME}_SOURCES
     main.cpp
     test_fpmath_float.cpp test_fpmath_float2.cpp test_fpmath_float4.cpp
-    test_intmath_int.cpp test_intmath_int2.cpp test_intmath_int4.cpp
-    test_intmath_long.cpp test_intmath_long2.cpp test_intmath_long4.cpp
+    test_intmath.cpp
     test_hiloeo.cpp test_local.cpp test_pointercast.cpp
     test_if.cpp test_loop.cpp
     test_readimage.cpp test_readimage_int16.cpp test_readimage_fp32.cpp