Current GIT Version still fails compile - this time in mmc_sdhci module. I didn't bother to fix this, waiting for the "official" fix.. Normal generic/server builds work fine.

Building custom xen...
make ARCH=x86_64 EXTRAVERSION=-11-xen SUBLEVEL=22 -C /usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-build-xen -j1
make[1]: Entering directory `/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-build-xen'
make -C /usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen O=/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-build-xen
  Using /usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen as source for kernel
  GEN     /usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-build-xen/Makefile
  CHK     include/linux/version.h
  CHK     include/linux/utsrelease.h
  CALL    /usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/scripts/checksyscalls.sh
  CHK     include/linux/compile.h
  CC [M]  drivers/mmc/mss/mss_sdhci.o
In file included from /usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:36:
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.h:237: error: field 'card_tasklet' has incomplete type
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.h:238: error: field 'finish_tasklet' has incomplete type
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c: In function 'sdhci_finish_data':
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:556: warning: implicit declaration of function 'tasklet_schedule'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c: In function 'sdhci_send_command':
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:627: warning: format '%08X' expects type 'unsigned int', but argument 3 has type 'long unsigned int'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c: At top level:
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1174: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'sdhci_irq'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c: In function 'sdhci_suspend':
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1281: warning: implicit declaration of function 'free_irq'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1267: warning: unused variable 'ret'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c: In function 'sdhci_resume':
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1312: warning: implicit declaration of function 'request_irq'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1312: error: 'sdhci_irq' undeclared (first use in this function)
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1312: error: (Each undeclared identifier is reported only once
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1312: error: for each function it appears in.)
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1313: error: 'IRQF_SHARED' undeclared (first use in this function)
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c: In function 'sdhci_probe_slot':
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1547: warning: implicit declaration of function 'tasklet_init'
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1554: error: 'sdhci_irq' undeclared (first use in this function)
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1554: error: 'IRQF_SHARED' undeclared (first use in this function)
/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-source-xen/drivers/mmc/mss/mss_sdhci.c:1585: warning: implicit declaration of function 'tasklet_kill'
make[6]: *** [drivers/mmc/mss/mss_sdhci.o] Error 1
make[5]: *** [drivers/mmc/mss] Error 2
make[4]: *** [drivers/mmc] Error 2
make[3]: *** [drivers] Error 2
make[2]: *** [_all] Error 2
make[1]: *** [all] Error 2
make[1]: Leaving directory `/usr/src/xen-kernel/ubuntu-gutsy/debian/build/custom-build-xen'
make: *** [/usr/src/xen-kernel/ubuntu-gutsy/debian/stamps/stamp-custom-build-xen] Fehler 2