When cross-compiling, get type sizes of the host system, not the build system.

This is Guile commit 24b30130ca75653bdbacea84ce0443608379d630, which
fixes <https://issues.guix.gnu.org/54198>, with one difference: it uses
8 instead of SIZEOF_INTMAX_T, such that we do not need to modify
'configure.ac' to check for the size of 'intmax_t' and to run 'autoreconf'
(libguile/numbers.c expects SCM_SIZEOF_INTMAX_T = 8).

diff --git a/libguile/gen-scmconfig.c b/libguile/gen-scmconfig.c
index 01b14f14d..691ebd0af 100644
--- a/libguile/gen-scmconfig.c
+++ b/libguile/gen-scmconfig.c
@@ -1,4 +1,4 @@
-/* Copyright 2003-2013,2018,2020,2021
+/* Copyright 2003-2013, 2018, 2020-2022
      Free Software Foundation, Inc.
 
    This file is part of Guile.
@@ -238,21 +238,21 @@ main (int argc, char *argv[])
   pf ("\n");
   pf ("/* Standard types. */\n");
 
-  pf ("#define SCM_SIZEOF_CHAR %zu\n", sizeof (char));
-  pf ("#define SCM_SIZEOF_UNSIGNED_CHAR %zu\n", sizeof (unsigned char));
-  pf ("#define SCM_SIZEOF_SHORT %zu\n", sizeof (short));
-  pf ("#define SCM_SIZEOF_UNSIGNED_SHORT %zu\n", sizeof (unsigned short));
-  pf ("#define SCM_SIZEOF_LONG %zu\n", sizeof (long));
-  pf ("#define SCM_SIZEOF_UNSIGNED_LONG %zu\n", sizeof (unsigned long));
-  pf ("#define SCM_SIZEOF_INT %zu\n", sizeof (int));
-  pf ("#define SCM_SIZEOF_UNSIGNED_INT %zu\n", sizeof (unsigned int));
-  pf ("#define SCM_SIZEOF_SIZE_T %zu\n", sizeof (size_t));
-  pf ("#define SCM_SIZEOF_LONG_LONG %zu\n", sizeof (long long));
-  pf ("#define SCM_SIZEOF_UNSIGNED_LONG_LONG %zu\n", sizeof (unsigned long long));
-  pf ("#define SCM_SIZEOF_INTMAX %zu\n", sizeof (intmax_t));
-  pf ("#define SCM_SIZEOF_SCM_T_PTRDIFF %zu\n", sizeof (ptrdiff_t));
-  pf ("#define SCM_SIZEOF_INTPTR_T %zu\n", sizeof (intptr_t));
-  pf ("#define SCM_SIZEOF_UINTPTR_T %zu\n", sizeof (uintptr_t));
+  pf ("#define SCM_SIZEOF_CHAR %d\n", SIZEOF_CHAR);
+  pf ("#define SCM_SIZEOF_UNSIGNED_CHAR %d\n", SIZEOF_UNSIGNED_CHAR);
+  pf ("#define SCM_SIZEOF_SHORT %d\n", SIZEOF_SHORT);
+  pf ("#define SCM_SIZEOF_UNSIGNED_SHORT %d\n", SIZEOF_UNSIGNED_SHORT);
+  pf ("#define SCM_SIZEOF_LONG %d\n", SIZEOF_LONG);
+  pf ("#define SCM_SIZEOF_UNSIGNED_LONG %d\n", SIZEOF_UNSIGNED_LONG);
+  pf ("#define SCM_SIZEOF_INT %d\n", SIZEOF_INT);
+  pf ("#define SCM_SIZEOF_UNSIGNED_INT %d\n", SIZEOF_UNSIGNED_INT);
+  pf ("#define SCM_SIZEOF_SIZE_T %d\n", SIZEOF_SIZE_T);
+  pf ("#define SCM_SIZEOF_LONG_LONG %d\n", SIZEOF_LONG_LONG);
+  pf ("#define SCM_SIZEOF_UNSIGNED_LONG_LONG %d\n", SIZEOF_UNSIGNED_LONG_LONG);
+  pf ("#define SCM_SIZEOF_INTMAX %d\n", 8); /* like SIZEOF_INTMAX_T */
+  pf ("#define SCM_SIZEOF_SCM_T_PTRDIFF %d\n", SIZEOF_PTRDIFF_T);
+  pf ("#define SCM_SIZEOF_INTPTR_T %d\n", SIZEOF_INTPTR_T);
+  pf ("#define SCM_SIZEOF_UINTPTR_T %d\n", SIZEOF_UINTPTR_T);
 
   pf ("\n");
   pf ("/* same as POSIX \"struct timespec\" -- always defined */\n");