The following compile warnings appear when using SPARCworks cc 4.2 on Solaris 2.6.  Most of them seem to be signed vs. unsigned char.

snprintf.c: empty translation unit
functions/gdttf.c: empty translation unit
functions/gdcache.c: empty translation unit
functions/dlist.c: empty translation unit
  [this warning just means that there is nothing left in the source file after removing comments
   and #ifdef's, not sure how one could eliminate it]
fopen-wrappers.c, line 933: warning: statement not reached
functions/file.c
 line 277, args 1 and 2: prototype mismatch (php3_string.h:103 (php3i_stristr) is uchar *, actual arg is char *)
 line 278, args 1 and 2: ""
 line 317, args 1 and 2: ""
functions/fsock.c
 line 209, arg 4: prototype mismatch (sys/socket.h:338 (getsockopt) is char *, arg is int *)
functions/gd.c
 line 1513, arg 1: prototype mismatch (string.h:64 (strlen) is const char *, arg is uchar *)
functions/image.c
 line 216, arg 1: prototype mismatch (stdio.h:258 (sprintf) is char *, arg is uchar *)
 line 218, args 2 and 3: prototype mismatch (internal_functions.h:75 (add_assoc_stringl) is char *, arg is uchar *)
 line 305: statement not reached
functions/iptc.c
 lines 298, 321: assignment type mismatch: char * = uchar *
 line 354, arg 1: prototype mismatch (stdio.h:258 (sprintf) is char *, arg is uchar *)
 line 366, arg 1: prototype mismatch (string.h:64 (strlen) is const char *, arg is uchar *)
 line 366, arg 2: prototype mismatch (php3_hash.h:119 (_php3_hash_find) is char *, arg is uchar *)
 line 372: same as line 366
 line 375, arg 2: prototype mismatch (internal_functions.h:84 (add_next_index_stringl) is char *, arg is uchar *)
functions/md5.c
 line 54, arg 2: prototype mismatch (functions/md5.h:69 (PHP3_MD5Update) is uchar *, arg is char *)
functions/string.c
 line 54: assignment type mismatch: uchar * = char *
 lines 56, 66, 619: return value type mismatch (function is declared to return char *, returns uchar *)
 line 83, arg 1: prototype mismatch (functions/string.c:49 (php_bin2hex) is const uchar *, arg is char *)
 line 643, args 1 and 2: prototype mismatch (functions/php3_string.h:103 (php3i_stristr) is uchar *, arg is char *)
functions/base64.c
 line 155, arg 1: prototype mismatch (functions/base64.h:37 (_php3_base64_encode) is uchar *, arg is char *)
 line 157: assignment type mismatch: char * = uchar *
 line 179, arg 1: prototype mismatch (functions/base64.h:38 (_php3_base64_decode) is uchar *, arg is char *)
 line 181: assignment type mismatch: char * = uchar *
functions/sysvshm.c, line 455: warning: statement not reached
functions/php3_mckcrypt.c
 line 96, arg 4: prototype mismatch: (mckcrypt.h:25 (mck_encr) is uchar *, arg is char *)
 line 108, arg 3: prototype mismatch (internal_functions.h:75 (add_assoc_stringl) is char *, arg is uchar *)
 line 110, arg 3: prototype mismatch (internal_functions.h:75 (add_assoc_stringl) is char *, arg is uchar *)
 line 151, arg 4: prototype mismatch: (mckcrypt.h:46 (mck_decr) is uchar *, arg is char *)
 line 163, arg 3: prototype mismatch (internal_functions.h:75 (add_assoc_stringl) is char *, arg is uchar *)
 line 165, arg 3: prototype mismatch (internal_functions.h:75 (add_assoc_stringl) is char *, arg is uchar *)