clean up cache size code

These warnings are avoidable:
In file included from ./m4ri/mzd.h:49:0,
                 from ./m4ri/mzp.h:31,
                 from ./m4ri/m4ri.h:56,
                 from testsuite/test_invert.c:3:
./m4ri/misc.h:575:0: warning: "__M4RI_CPU_L3_CACHE" redefined [enabled by default]
 #define __M4RI_CPU_L3_CACHE 4194304
 ^
In file included from ./m4ri/mzd.h:39:0,
                 from ./m4ri/mzp.h:31,
                 from ./m4ri/m4ri.h:56,
                 from testsuite/test_invert.c:3:
./m4ri/m4ri_config.h:11:0: note: this is the location of the previous definition
 #define __M4RI_CPU_L3_CACHE  0
 ^
In file included from ./m4ri/mzd.h:49:0,
                 from ./m4ri/mzp.h:31,
                 from ./m4ri/m4ri.h:56,
                 from testsuite/test_invert.c:3:
./m4ri/misc.h:584:0: warning: "__M4RI_CPU_L2_CACHE" redefined [enabled by default]
 #define __M4RI_CPU_L2_CACHE 262144
 ^
In file included from ./m4ri/mzd.h:39:0,
                 from ./m4ri/mzp.h:31,
                 from ./m4ri/m4ri.h:56,
                 from testsuite/test_invert.c:3:
./m4ri/m4ri_config.h:10:0: note: this is the location of the previous definition
 #define __M4RI_CPU_L2_CACHE  0
Comments (1)
