It's actually not my setup - it's a user of my Freeciv package in the 'fink' environment. But yeah, i'm fairly certain that he's on x86_64. I'll send him a new patch and see what happens. It won't happen right away though, as i've got some calculus homework coming due. If the patch suppresses the warning, upstream probably should be notified that their assumptions as to what will tolerated are out of date...

Judging by the new title of the ticket, the other two warnings treated as errors are still going to be handled on this ticket. In that case, here is more detail on the third error he saw:

/bin/sh ../libtool --preserve-dup-deps --silent --tag=CC --mode=compile
llvm-gcc-4.2 -DHAVE_CONFIG_H -I. -I.. -I/sw/include
-DLOCALEDIR="\"/sw/share/locale\"" -DBINDIR="\"/sw/bin\""
-DDEFAULT_DATA_PATH="\".:data:~/.freeciv/2.3:/sw/share/freeciv\""
-DDEFAULT_SAVES_PATH="\"\""
-DDEFAULT_SCENARIO_PATH="\".:data/scenario:~/.freeciv/2.3/scenarios:~/.freeciv/scenarios:/sw/share/freeciv/scenario\""
-Wall -Wpointer-arith -Wcast-align -Wmissing-prototypes
-Wmissing-declarations -Werror -g -O2 -c -o registry.lo registry.c
cc1: warnings being treated as errors
registry.c: In function 'secfile_entry_delete':
registry.c:1713: warning: return makes integer from pointer without a cast
registry.c: In function 'secfile_lookup_plain_enum_full':
registry.c:2116: warning: return makes integer from pointer without a cast
registry.c:2117: warning: return makes integer from pointer without a cast
registry.c:2118: warning: return makes integer from pointer without a cast
registry.c:2119: warning: return makes integer from pointer without a cast
registry.c: In function 'secfile_lookup_bitwise_enum_full':
registry.c:2258: warning: return makes integer from pointer without a cast
registry.c:2259: warning: return makes integer from pointer without a cast
registry.c:2260: warning: return makes integer from pointer without a cast
registry.c:2261: warning: return makes integer from pointer without a cast
registry.c: In function 'secfile_lookup_enum_data':
registry.c:2440: warning: return makes integer from pointer without a cast
registry.c:2441: warning: return makes integer from pointer without a cast
registry.c:2442: warning: return makes integer from pointer without a cast

> If so, we could avoid the warning by adding some sort of clang
> detection in that #if. (Alternatively, by turning off
> -Wcast-align for clang, but that's likely to be fiddlier and may
> hide issues we're interested in.)

The hyper proper way would be to make configure check instead of listing environments with known properties in that #if.

Neither the shared.c error or the md5.c error appear without --enable-debug, so perhaps i named this ticket incorrectly. Actually i've just collected a third warning that pops up in this environment. Should i split out the new one and the 'comparison of unsigned expression' problem into separate tickets?

My package does set --enable-debug, but i thought the user in question had deleted that line. I don't currently have access to 10.7, so i'm awaiting his response.

Clang is now the default compiler on OSX 10.7 A.K.A Lion, and also OSX 10.6 A.K.A Snow Leopard with the optional XCode 4.2 update. On those systems, an ordinary make fails like so:

/bin/sh ../libtool --preserve-dup-deps --silent --tag=CC --mode=compile
gcc -DHAVE_CONFIG_H -I. -I.. -I/sw/include
-DLOCALEDIR="\"/sw/share/locale\"" -DBINDIR="\"/sw/bin\""
-DDEFAULT_DATA_PATH="\".:data:~/.freeciv/2.3:/sw/share/freeciv\""
-DDEFAULT_SAVES_PATH="\"\""
-DDEFAULT_SCENARIO_PATH="\".:data/scenario:~/.freeciv/2.3/scenarios:~/.freeciv/scenarios:/sw/share/freeciv/scenario\""
-Wall -Wpointer-arith -Wcast-align -Wmissing-prototypes
-Wmissing-declarations -Wno-unused-but-set-variable -Werror -g -O2
-fsigned-char -c -o shared.lo shared.c
shared.c:370:36: error: comparison of unsigned expression >= 0 is always
true [-Werror,-Wtautological-compare]
while (mantissa != 0 && exponent >= 0) {
~~~~~~~~ ^ ~
/bin/sh ../libtool --preserve-dup-deps --silent --tag=CC --mode=compile
gcc -DHAVE_CONFIG_H -I. -I.. -I/sw/include
-DLOCALEDIR="\"/sw/share/locale\"" -DBINDIR="\"/sw/bin\""
-DDEFAULT_DATA_PATH="\".:data:~/.freeciv/2.3:/sw/share/freeciv\""
-DDEFAULT_SAVES_PATH="\"\""
-DDEFAULT_SCENARIO_PATH="\".:data/scenario:~/.freeciv/2.3/scenarios:~/.freeciv/scenarios:/sw/share/freeciv/scenario\""
-Wall -Wpointer-arith -Wcast-align -Wmissing-prototypes
-Wmissing-declarations -Wno-unused-but-set-variable -Werror -g -O2
-fsigned-char -c -o md5.lo md5.c
md5.c:148:5: error: cast from 'const unsigned char ' to 'MD5_u32plus '
(aka 'unsigned int *') increases required alignment from 1 to 4
[-Werror,-Wcast-align]
STEP(F, a, b, c, d, SET(0), 0xd76aa478, 7)
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The workaround for now is to force usage of the less strict llvm compiler, though i expect clang usage is going to become more widespread.