Compiling fails

[Simonas Kazlauskas <s@kazlauskas.me>]

Compiling current HEAD (as of 2013-04-18 13:20) fails with following
error:

    CXX -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 lib/parse-time-vrp.o
    In file included from lib/parse-time-vrp.cc:23:
    In file included from ./lib/database-private.h:33:
    ./lib/notmuch-private.h:478:8: error: visibility does not match previous declaration
    struct visible _notmuch_string_list {
           ^
    ./lib/notmuch-private.h:67:33: note: expanded from macro 'visible'
    # define visible __attribute__((visibility("default")))
                                    ^
    ./lib/notmuch-private.h:52:13: note: previous attribute is here
    #pragma GCC visibility push(hidden)
                ^
    In file included from lib/database.cc:21:
    In file included from ./lib/database-private.h:33:
    ./lib/notmuch-private.h:478:8: error: visibility does not match previous declaration
    struct visible _notmuch_string_list {
           ^
    ./lib/notmuch-private.h:67:33: note: expanded from macro 'visible'
    # define visible __attribute__((visibility("default")))
                                    ^
    ./lib/notmuch-private.h:52:13: note: previous attribute is here
    #pragma GCC visibility push(hidden)
                ^
    1 error generated.
    make: *** [lib/parse-time-vrp.o] Error 1
    make: *** Waiting for unfinished jobs....
    1 error generated.
    make: *** [lib/database.o] Error 1

Of course `#pragma GCC` has to mean something and might be a reason why
compiling with `CXX=clang++` fails.