Remove '-mcmodel=small' and '-mno-red-zone' from LIB_COMPILER_FLAGS (#229)

* Fix reallocarray and use 'rm -f' when cleaning.

In sys/src/lib.json: use 'rm -f' when removing object files.
In sys/src/libc/port/reallocarray.c: Actually make this build
under Harvey. :-)

Signed-off-by: Dan Cross <cross@gajendra.net>

* Remove '-mcmodel=small' and '-mno-red-zone' from LIB_COMPILER_FLAGS

Signed-off-by: Dan Cross <cross@gajendra.net>

sys/src/FLAGS

@@ -61,8 +61,6 @@ LIB_COMPILER_FLAGS = [
     "-g",
     "-gdwarf-2",
     "-ggdb",
-    "-mcmodel=small",
-    "-mno-red-zone",
     "-O0",
     "-static",
     "-Wall",