I think I solved bug 49208 [1] (failure to create any process on empty Wine prefix under build-dependant circumstances) but I am a bit unsure on the proper fix.
The failure is triggered when kernelbase.dll size exceeds 0x410000. If that happens, it does not fit in 0x7b000000 - 0x0x7b410000 range (where 0x7b410000 is kernel32.dll.so load address), and goes in the lower address space, so a bit later an .exe without relocations cannot be mapped to 0x40000.
The issue is fixed by 'strip kernelbase.dll' for me. Fitting kernelbase.dll into 0x410000 seems correct to me, but I am not sure about the best way to guarantee that.