Avoid creating spurious non-suffixed c/zgemm_kernels

Plain cgemm_kernel and zgemm_kernel are not used anywhere, only cgemm_kernel_b etc.
Needlessly building them (without any define like NN, CN, etc.) just happened to work on most platforms, but not on arm64. See #1870

kernel/CMakeLists.txt

@@ -125,10 +125,13 @@ function (build_core TARGET_CORE KDIR TSUFFIX KERNEL_DEFINITIONS)
       set(USE_TRMM true)
     endif ()
 
-    foreach (float_type ${FLOAT_TYPES})
+    foreach (float_type SINGLE DOUBLE)
       string(SUBSTRING ${float_type} 0 1 float_char)
       GenerateNamedObjects("${KERNELDIR}/${${float_char}GEMMKERNEL}" "" "gemm_kernel" false "" "" false ${float_type})
+    endforeach()
 
+    foreach (float_type ${FLOAT_TYPES})
+      string(SUBSTRING ${float_type} 0 1 float_char)
       if (${float_char}GEMMINCOPY)
         GenerateNamedObjects("${KERNELDIR}/${${float_char}GEMMINCOPY}" "${float_type}" "${${float_char}GEMMINCOPYOBJ}" false "" "" true ${float_type})
       endif ()