cmake: Fix check for symbols size_t and off_t

The two issues with the previous approach were that:

1. `check_symbol_exists` would store "1" or "" into
   variable `off_t` rather than string "off_t", and

2. (`check_symbol_exists` would not find `off_t` or
   `size_t` on modern Linux).

Was reported with NetBSD 9.3.

`size_t` is part of C99 (which Expat requires), so
only the `off_t` half remains.

.github/workflows/data/expat_config_h_cmake__expected.txt

@@ -27,7 +27,6 @@ PACKAGE_STRING
 PACKAGE_TARNAME
 PACKAGE_URL
 PACKAGE_VERSION
-size_t
 STDC_HEADERS
 WORDS_BIGENDIAN
 XML_ATTR_INFO

.github/workflows/data/expat_config_h_in__expected.txt

@@ -31,7 +31,6 @@ PACKAGE_STRING
 PACKAGE_TARNAME
 PACKAGE_URL
 PACKAGE_VERSION
-size_t
 STDC_HEADERS
 VERSION
 WORDS_BIGENDIAN

expat/ConfigureChecks.cmake

@@ -46,12 +46,18 @@ else(WORDS_BIGENDIAN)
 endif(WORDS_BIGENDIAN)
 
 if(HAVE_SYS_TYPES_H)
-    check_symbol_exists("off_t" "sys/types.h" off_t)
-    check_symbol_exists("size_t" "sys/types.h" size_t)
-else(HAVE_SYS_TYPES_H)
+    check_c_source_compiles("
+        #include <sys/types.h>
+        int main(void) {
+            const off_t offset = -123;
+            return 0;
+        }"
+        HAVE_OFF_T)
+endif()
+
+if(NOT HAVE_OFF_T)
     set(off_t "long")
-    set(size_t "unsigned")
-endif(HAVE_SYS_TYPES_H)
+endif()
 
 check_c_source_compiles("
         #include <stdlib.h>  /* for NULL */

expat/configure.ac

@@ -160,7 +160,6 @@ AC_C_BIGENDIAN([AC_DEFINE([WORDS_BIGENDIAN], 1)
 AC_DEFINE_UNQUOTED([BYTEORDER], $BYTEORDER, [1234 = LILENDIAN, 4321 = BIGENDIAN])
 
 AC_C_CONST
-AC_TYPE_SIZE_T
 
 AC_ARG_WITH([xmlwf],
   [AS_HELP_STRING([--without-xmlwf], [do not build xmlwf])],

expat/expat_config.h.cmake

@@ -119,7 +119,4 @@
 /* Define to `long' if <sys/types.h> does not define. */
 #cmakedefine off_t @off_t@
 
-/* Define to `unsigned' if <sys/types.h> does not define. */
-#cmakedefine size_t @size_t@
-
 #endif // ndef EXPAT_CONFIG_H