minor cmake fix for header only use-case (oneMKL in particular)

CMakeLists.txt

@@ -109,7 +109,8 @@ option(BLAS_ENABLE_EXTENSIONS "Whether to enable portBLAS extensions" ON)
 option(BLAS_ENABLE_COMPLEX "Whether to enable complex data type for GEMM" OFF)
 option(BLAS_ENABLE_HALF "Whether to enable sycl::half data type for supported operators" OFF)
 
-if(${TUNING_TARGET} STREQUAL "DEFAULT_CPU")
+if(((NOT INSTALL_HEADER_ONLY) AND (TUNING_TARGET STREQUAL "DEFAULT_CPU"))
+    OR (INSTALL_HEADER_ONLY AND (NOT TUNING_TARGET)))
   set(BLAS_ENABLE_HALF OFF)
   message(STATUS "FP16 operations are not supported for CPU targets. BLAS_ENABLE_HALF is disabled")
 endif()