Disable flang (over-)optimizations in BLAS tests (#3600)

* limit flang optimizations to -O2

test/CMakeLists.txt

@@ -5,7 +5,9 @@ enable_language(Fortran)
 if (CMAKE_Fortran_COMPILER_ID STREQUAL GNU)
         set(CMAKE_Fortran_FLAGS "${CMAKE_Fortran_FLAGS} -fno-tree-vectorize")
 endif()
-
+if (CMAKE_Fortran_COMPILER_ID STREQUAL Flang)
+	set(CMAKE_Fortran_FLAGS "$CMAKE_Fortran_FLAGS -O2")
+endif()
 
 if (BUILD_SINGLE)
 	list( APPEND OpenBLAS_Tests sblat1 sblat2 sblat3)