add namespace-protected name for sysinfo function

it will be needed to implement some things in sysconf, and the syscall
can't easily be used directly because the x32 syscall uses the wrong
structure layout. the l (uncreative, for "linux") prefix is used since
the symbol name __sysinfo is already taken for AT_SYSINFO from the aux
vector.

the way the x32 override of this function works is also changed to be
simpler and avoid the useless jump instruction.

src/linux/sysinfo.c

@@ -1,7 +1,10 @@
 #include <sys/sysinfo.h>
 #include "syscall.h"
+#include "libc.h"
 
-int sysinfo(struct sysinfo *info)
+int __lsysinfo(struct sysinfo *info)
 {
 	return syscall(SYS_sysinfo, info);
 }
+
+weak_alias(__lsysinfo, sysinfo);

src/linux/x32/sysinfo.s

@@ -1,5 +1 @@
-.text
-.global sysinfo
-.type   sysinfo,@function
-sysinfo:
-	jmp __x32_sysinfo
+# see arch/x32/src/sysinfo.c