[PATCH] x86/pv: Fix Clang build with !CONFIG_PV32

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Clang 3.5 doesn't do enough dead-code-elimination to drop the compat_gdt
reference, resulting in a linker failure:

  hidden symbol `per_cpu__compat_gdt' isn't defined

Drop the local variable, and move evaluation of this_cpu(compat_gdt) to within
the guarded region.

Reported-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/cpu/common.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 131ff03fcf..63f3893c7a 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -711,8 +711,6 @@ void load_system_tables(void)
        struct tss64 *tss = &this_cpu(tss_page).tss;
        seg_desc_t *gdt =
                this_cpu(gdt) - FIRST_RESERVED_GDT_ENTRY;
-       seg_desc_t *compat_gdt =
-               this_cpu(compat_gdt) - FIRST_RESERVED_GDT_ENTRY;
 
        const struct desc_ptr gdtr = {
                .base = (unsigned long)gdt,
@@ -753,8 +751,9 @@ void load_system_tables(void)
        _set_tssldt_desc(gdt + TSS_ENTRY, (unsigned long)tss,
                         sizeof(*tss) - 1, SYS_DESC_tss_avail);
        if ( IS_ENABLED(CONFIG_PV32) )
-               _set_tssldt_desc(compat_gdt + TSS_ENTRY, (unsigned long)tss,
-                                sizeof(*tss) - 1, SYS_DESC_tss_busy);
+               _set_tssldt_desc(
+                       this_cpu(compat_gdt) - FIRST_RESERVED_GDT_ENTRY + 
TSS_ENTRY,
+                       (unsigned long)tss, sizeof(*tss) - 1, 
SYS_DESC_tss_busy);
 
        per_cpu(full_gdt_loaded, cpu) = false;
        lgdt(&gdtr);
-- 
2.11.0