Sorry, wrong link. It should have been:
Line 215 of http://cgit.freedesktop.org/xorg/driver/glamor/tree/src/glamor_fbo.c

This leads to:

Fatal server error:
[430338.463] (EE) (EE) BUG: triggered 'if (f[f_idx])'
[430338.463] (EE) BUG: log.c:464 in pnprintf()
[430338.463] (EE) Unsupported printf directive '#'
[430338.463] (EE) 
[430338.463] (EE) Backtrace:
[430338.463] (EE) 0: /usr/bin/X (xorg_backtrace+0x3d) [0x57f67d]
[430338.463] (EE) 1: /usr/bin/X (LogVMessageVerbSigSafe+0x87d) [0x58aefd]
[430338.463] (EE) 2: /usr/bin/X (FatalError+0xd5) [0x58b1c5]
[430338.463] (EE) 3: /usr/lib/libglamor.so.0 (0x7f65e8861000+0x25edf) [0x7f65e8886edf]
[430338.463] (EE) 4: /usr/lib/libglamor.so.0 (0x7f65e8861000+0x2603e) [0x7f65e888703e]
[430338.463] (EE) 5: /usr/lib/libglamor.so.0 (glamor_create_pixmap+0x298) [0x7f65e88653f8]
[430338.463] (EE) 6: /usr/lib/xorg/modules/drivers/radeon_drv.so (0x7f65e5d33000+0x4bc23) [0x7f65e5d7ec23]
[430338.463] (EE) 7: /usr/bin/X (0x400000+0x33317) [0x433317]
[430338.463] (EE) 8: /usr/bin/X (0x400000+0x373be) [0x4373be]
[430338.463] (EE) 9: /usr/bin/X (0x400000+0x2693a) [0x42693a]
[430338.463] (EE) 10: /usr/lib/libc.so.6 (__libc_start_main+0xf5) [0x7f65ea213bc5]
[430338.463] (EE) 11: /usr/bin/X (0x400000+0x26c81) [0x426c81]
[430338.463] (EE) 
[430338.463] destination is framebuffer incomplete: unknown error [%#x]
[430338.463] (EE) 
[430338.463] (EE) 
Please consult the The X.Org Foundation support 
         at http://wiki.x.org

Could you tell more detail about how to trigger the following bug?
Actually, this means there is another bug besides this unsupported printf directive. May be you can file a new bug for that.

(In reply to comment #2)
> This leads to:
> 
> Fatal server error:
> [430338.463] (EE) (EE) BUG: triggered 'if (f[f_idx])'
> [430338.463] (EE) BUG: log.c:464 in pnprintf()
> [430338.463] (EE) Unsupported printf directive '#'
> [430338.463] (EE) 
> [430338.463] (EE) Backtrace:
> [430338.463] (EE) 0: /usr/bin/X (xorg_backtrace+0x3d) [0x57f67d]
> [430338.463] (EE) 1: /usr/bin/X (LogVMessageVerbSigSafe+0x87d) [0x58aefd]
> [430338.463] (EE) 2: /usr/bin/X (FatalError+0xd5) [0x58b1c5]
> [430338.463] (EE) 3: /usr/lib/libglamor.so.0 (0x7f65e8861000+0x25edf)
> [0x7f65e8886edf]
> [430338.463] (EE) 4: /usr/lib/libglamor.so.0 (0x7f65e8861000+0x2603e)
> [0x7f65e888703e]
> [430338.463] (EE) 5: /usr/lib/libglamor.so.0 (glamor_create_pixmap+0x298)
> [0x7f65e88653f8]
> [430338.463] (EE) 6: /usr/lib/xorg/modules/drivers/radeon_drv.so
> (0x7f65e5d33000+0x4bc23) [0x7f65e5d7ec23]
> [430338.463] (EE) 7: /usr/bin/X (0x400000+0x33317) [0x433317]
> [430338.463] (EE) 8: /usr/bin/X (0x400000+0x373be) [0x4373be]
> [430338.463] (EE) 9: /usr/bin/X (0x400000+0x2693a) [0x42693a]
> [430338.463] (EE) 10: /usr/lib/libc.so.6 (__libc_start_main+0xf5)
> [0x7f65ea213bc5]
> [430338.463] (EE) 11: /usr/bin/X (0x400000+0x26c81) [0x426c81]
> [430338.463] (EE) 
> [430338.463] destination is framebuffer incomplete: unknown error [%#x]
> [430338.463] (EE) 
> [430338.463] (EE) 
> Please consult the The X.Org Foundation support 
>          at http://wiki.x.org

Yes, there is another bug. Either my X server crashes with this backtrace or with this https://bugs.freedesktop.org/show_bug.cgi?id=71161 backtrace. I am not sure if they are related.