From Debian user Falk Hueffner <falk@debian.org>:

[...]
gcc -DHAVE_CONFIG_H -I. -I.. -I../gl -I../intl -DLOCALEDIR=\"/usr/share/locale\"
+-DGNUPG_BINDIR="\"/usr/bin\"" -DGNUPG_LIBEXECDIR="\"/usr/lib/gnupg2\""
+-DGNUPG_LIBDIR="\"/usr/lib/gnupg\"" -DGNUPG_DATADIR="\"/usr/share/gnupg\""
+-DGNUPG_SYSCONFDIR="\"/usr/etc/gnupg\"" -I/usr/include
+-DWITHOUT_GNU_PTH=1 -Wall -g -O2 -Wall -Wcast-align -Wshadow -Wstrict-prototypes
+-Wformat -Wno-format-y2k -Wformat-security -Wno-pointer-sign -Wpointer-arith -MT
+libcommon_a-estream-printf.o -MD -MP -MF .deps/libcommon_a-estream-printf.Tpo -c
+-o libcommon_a-estream-printf.o `test -f 'estream-printf.c' || echo
+'./'`estream-printf.c
estream-printf.c: In function 'read_values':
estream-printf.c:711: error: wrong type argument to unary exclamation mark
make[3]: *** [libcommon_a-estream-printf.o] Error 1
make[3]: Leaving directory `/build/buildd/gnupg2-2.0.5/common'
[...]

Full log at
http://buildd.debian.org/fetch.cgi?&pkg=gnupg2&ver=2.0.5-1&arch=alpha&stamp=118662
+6239&file=log

The reason is

static int read_values (valueitem_t valuetable, size_t valuetable_len, va_list
+vaargs) {
[...]

if (!vaargs)

"!vaargs" simply doesn't make any sense, I have no idea what it is
supposed to do. It just happens to compile on many architectures,
where va_list is a pointer.