Specifying additional flags for the default compiler

At present, only the Level 2 kernels have this option. It's the same as when you specify a new compiler and flags, but you specify the compiler as `+', and the flags you give on the following flagline are added to its default flags. This can be useful for compiling the same routine multiple times with differing macros (eg., prefetch distance, etc.). Let us say you had this simple gemv description file:

2
  1  8  0  0 ATL_gemvN_mm.c     "R. Clint Whaley"
  2  0  1  1 ATL_gemvN_1x1_1.c  "R. Clint Whaley"
2
101 8  0  0 ATL_gemvT_mm.c      "R. Clint Whaley"
102 0  2  8 ATL_gemvT_2x8_0.c   "R. Clint Whaley"

You now want to compile ATL_gemvT_2x8_0.c two different ways: one with a default prefetch distance, and once with a prefetch distance of 16. This would be simply:

2
  1  8  0  0 ATL_gemvN_mm.c     "R. Clint Whaley"
  2  0  1  1 ATL_gemvN_1x1_1.c  "R. Clint Whaley"
2
101 8  0  0 ATL_gemvT_mm.c      "R. Clint Whaley"
102 0  2  8 ATL_gemvT_2x8_0.c   "R. Clint Whaley"
103 0  2  8 ATL_gemvT_2x8_0.c   "R. Clint Whaley" \
+
-DPREFETCH_DIST=16