If you remove "inline" from mediatek/kernel/drivers/combo/drv_wlan/mt6628/wlan/os/linux/include/gl_kal.h in line 1859, it continues compiling. Usually removing an "inline" shouldn't break a program, but it might be different when you are modifying possibly time critical kernel code.
TARGET_BUILD_VARIANT=user TARGET_PRODUCT=ahong89_wet_jb2 MTK_ROOT_CUSTOM=../mediatek/custom/ make
Notice: I think that normally on MTK kernels you also have to set the TARGET_BUILD_VARIANT, otherwise pvr drivers won't load.
UPDATE: the kernel source doesn't boot when I tried to do a recovery. http://pastebin.com/raw.php?i=4bv6fyWw
I had to strip a few things away to make the kernel smaller, but I don't think this is causing this... Hmmm.
UPDATE2: I tried to boot with original kernel settings and with, without TARGET_BUILD_VARIANT. It doesn't seem to boot.