When compiling 64-bit with Sun WorkShop 5.0 cc the httpd binary aborts with 'Bus Error'.
To correct the problem you must change all 'int' variable declarations to 'long'
for 'struct php_assert_globals'  in lines 27-34 of file 'ext/standard/assert.c':

   typedef struct {
=>        long active;
=>        long bail;
=>        long warning;
=>        long quiet_eval;
             char *default_callback;
             char *callback;
  } php_assert_globals;

There is also a configuration problem. While in 32-bit the 'configure' script sets '#define PHP_STD_DES_CRYPT 1' in file 'php_config.h' it does not do the same in 64-bit. You must change the value by hand in order to make a successful compilation.
I have successfully build PHP4RC1 with apache_1.3.12 under Solaris 7 in both the 32-bit and 64-bit environment and both statically and dynamically as a dso without other problems.