introduce sqrt_approx() in -lsys

. use this to avoid -lm dependency in mfs

lib/libsys/Makefile

@@ -57,6 +57,7 @@ SRCS=  \
 	sef_signal.c \
 	ser_putc.c \
 	spin.c \
+	sqrt_approx.c \
 	stacktrace.c \
 	sys_abort.c \
 	sys_clear.c \
@@ -127,6 +128,7 @@ SRCS=  \
 	vm_yield_get_block.c \
 	vprintf.c \
 
+
 CPPFLAGS.sched_start.c+=	-I${MINIXSRCDIR}
 
 .if (${NBSD_LIBC} != "no")

lib/libsys/sqrt_approx.c

@@ -0,0 +1,14 @@
+#include <minix/sysutil.h>
+
+u32_t sqrt_approx(u32_t in)
+{
+        int b, v = 0;
+        for(b = (sizeof(in)*8)/2-1; b >= 0; b--) {
+                u32_t n = v | (1UL << b);
+                if(n*n <= in)
+                        v = n;
+        }
+
+        return v;
+}
+