cc/gcc: do not build manuals in parallel

Reported-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Reported-by: Johannes Stezenbach <js@sig21.net>
Tested-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
(transplanted from c800b7d6a50c267c3e0a64829da4b082e260deff)

 # m68k specific configuration file

 ## depends on EXPERIMENTAL

 ##

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_BE

 ## select ARCH_SUPPORTS_WITH_CPU

 ##

 ## help The m68k architecture