use weak aliase rather than weak reference for vdso clock_gettime

this works around pcc's lack of working support for weak references,
and in principle is nice because it gets us back to the stage where
the only weak symbol feature we use is weak aliases, nothing else.

having fewer dependencies on fancy linker features is a good thing.

src/time/clock_gettime.c

@@ -4,17 +4,11 @@
 #include "syscall.h"
 #include "libc.h"
 
-int __vdso_clock_gettime(clockid_t, struct timespec *) __attribute__((weak));
-static int (*cgt)(clockid_t, struct timespec *) = __vdso_clock_gettime;
-
-int __clock_gettime(clockid_t clk, struct timespec *ts)
+static int sc_clock_gettime(clockid_t clk, struct timespec *ts)
 {
-	int r;
-	if (cgt) return cgt(clk, ts);
-	r = __syscall(SYS_clock_gettime, clk, ts);
+	int r = __syscall(SYS_clock_gettime, clk, ts);
 	if (!r) return r;
 	if (r == -ENOSYS) {
-		cgt = 0;
 		if (clk == CLOCK_REALTIME) {
 			__syscall(SYS_gettimeofday, clk, ts, 0);
 			ts->tv_nsec = (int)ts->tv_nsec * 1000;
@@ -26,4 +20,14 @@ int __clock_gettime(clockid_t clk, struct timespec *ts)
 	return -1;
 }
 
+weak_alias(sc_clock_gettime, __vdso_clock_gettime);
+
+int (*__cgt)(clockid_t, struct timespec *) = __vdso_clock_gettime;
+
+int __clock_gettime(clockid_t clk, struct timespec *ts)
+{
+	/* Conditional is to make this work prior to dynamic linking */
+	return __cgt ? __cgt(clk, ts) : sc_clock_gettime(clk, ts);
+}
+
 weak_alias(__clock_gettime, clock_gettime);