x86/xen: add prototypes for paravirt mmu functions

The paravirt MMU functions called via the PV_CALLEE_SAVE_REGS_THUNK()
macro can't be defined to be static, as the macro is generating a
function via asm() statement calling the paravirt MMU function.

In order to avoid warnings when specifying "-Wmissing-prototypes" for
the build, add local prototypes (there should never be any external
caller of those functions).
Reported-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Link: https://lore.kernel.org/r/20230614073501.10101-2-jgross@suse.comSigned-off-by: Juergen Gross <jgross@suse.com>

arch/x86/xen/mmu_pv.c

@@ -86,6 +86,22 @@
 #include "mmu.h"
 #include "debugfs.h"
 
+/*
+ * Prototypes for functions called via PV_CALLEE_SAVE_REGS_THUNK() in order
+ * to avoid warnings with "-Wmissing-prototypes".
+ */
+pteval_t xen_pte_val(pte_t pte);
+pgdval_t xen_pgd_val(pgd_t pgd);
+pmdval_t xen_pmd_val(pmd_t pmd);
+pudval_t xen_pud_val(pud_t pud);
+p4dval_t xen_p4d_val(p4d_t p4d);
+pte_t xen_make_pte(pteval_t pte);
+pgd_t xen_make_pgd(pgdval_t pgd);
+pmd_t xen_make_pmd(pmdval_t pmd);
+pud_t xen_make_pud(pudval_t pud);
+p4d_t xen_make_p4d(p4dval_t p4d);
+pte_t xen_make_pte_init(pteval_t pte);
+
 #ifdef CONFIG_X86_VSYSCALL_EMULATION
 /* l3 pud for userspace vsyscall mapping */
 static pud_t level3_user_vsyscall[PTRS_PER_PUD] __page_aligned_bss;