x86: properly define size_t

Having it defined unilaterally as 'unsigned long' got me surprised
recently when I tried to use the 'z' printk type modifier, as that is
expected by the compiler to be used only on the type it knows size_t
is supposed to have.

Generally the compiler provides a construct to do this, so use it when
available.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/microcode_amd.c
+++ b/xen/arch/x86/microcode_amd.c
@@ -183,10 +183,10 @@ static int get_next_ucode_from_buffer_am
     struct microcode_amd *mc_amd,
     const void *buf,
     size_t bufsize,
-    unsigned long *offset)
+    size_t *offset)
 {
     const uint8_t *bufp = buf;
-    unsigned long off;
+    size_t off;
     const struct mpbhdr *mpbuf;
 
     off = *offset;
@@ -203,7 +203,7 @@ static int get_next_ucode_from_buffer_am
         return -EINVAL;
     }
 
-    printk(KERN_DEBUG "microcode: size %lu, block size %u, offset %ld\n",
+    printk(KERN_DEBUG "microcode: size %zu, block size %u, offset %zu\n",
            bufsize, mpbuf->len, off);
 
     if ( (off + mpbuf->len) > bufsize )
@@ -234,7 +234,7 @@ static int get_next_ucode_from_buffer_am
 static int install_equiv_cpu_table(
     struct microcode_amd *mc_amd,
     const uint32_t *buf,
-    unsigned long *offset)
+    size_t *offset)
 {
     const struct mpbhdr *mpbuf = (const struct mpbhdr *)&buf[1];
 
--- a/xen/include/asm-x86/types.h
+++ b/xen/include/asm-x86/types.h
@@ -47,7 +47,13 @@ typedef unsigned long paddr_t;
 #define PRIpaddr "016lx"
 #endif
 
+#if defined(__SIZE_TYPE__)
+typedef __SIZE_TYPE__ size_t;
+#elif defined(__i386__)
+typedef unsigned int size_t;
+#else
 typedef unsigned long size_t;
+#endif
 
 typedef char bool_t;
 #define test_and_set_bool(b)   xchg(&(b), 1)