gcc-9: properly declare the {pv,hv}clock_page storage

The pvlock_page and hvclock_page variables are (as the name implies)
addresses to pages, created by the linker script.

But we declared them as just "extern u8" variables, which _works_, but
now that gcc does some more bounds checking, it causes warnings like

    warning: array subscript 1 is outside array bounds of ‘u8[1]’

when we then access more than one byte from those variables.

Fix this by simply making the declaration of the variables match
reality, which makes the compiler happy too.
Signed-off-by: NLinus Torvalds <torvalds@-linux-foundation.org>

arch/x86/entry/vdso/vclock_gettime.c

@@ -29,12 +29,12 @@ extern int __vdso_gettimeofday(struct timeval *tv, struct timezone *tz);
 extern time_t __vdso_time(time_t *t);
 
 #ifdef CONFIG_PARAVIRT_CLOCK
-extern u8 pvclock_page
+extern u8 pvclock_page[PAGE_SIZE]
 	__attribute__((visibility("hidden")));
 #endif
 
 #ifdef CONFIG_HYPERV_TSCPAGE
-extern u8 hvclock_page
+extern u8 hvclock_page[PAGE_SIZE]
 	__attribute__((visibility("hidden")));
 #endif