swtpm: Fix build error on 32bit systems due to inconsistent _FILE_OFFSET_BITS

Fix the following build error due to missing include of config.h where
_FILE_OFFSET_BITS is defined and leads to different sizes of off_t depending
on whether it is defined and/or included:

tpmlib.h:76:7: error: type of 'tpmlib_handle_tcg_tpm2_cmd_header' does not match original declaration [-Werror=lto-type-mismatch]
   76 | off_t tpmlib_handle_tcg_tpm2_cmd_header(const unsigned char *command,
      |       ^
tpmlib.c:576:7: note: return value type mismatch
  576 | off_t tpmlib_handle_tcg_tpm2_cmd_header(const unsigned char *command,
      |       ^
tpmlib.c:576:7: note: 'tpmlib_handle_tcg_tpm2_cmd_header' was previously declared here
tpmlib.c:576:7: note: code may be misoptimized unless '-fno-strict-aliasing' is used
lto1: all warnings being treated as errors
lto-wrapper: fatal error: gcc returned 1 exit status

Link: https://bugzilla.redhat.com/show_bug.cgi?id=2334600
Fixes: 599e2436d4 ("configure.ac: enable 64-bit file API on 32-bit systems")
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>