Jamfiles shouldn't use -Wall

[kaliber]

BuildSetup defines default warning flags, but some of Jamfiles adds its own. If -Wall is added then it could re-enable some warnings. For example:

BuildSetup defines:

HAIKU_WARNING_CCFLAGS = -Wall -Wno-trigraphs ...
src/add-ons/kernel/drivers/network/etherpci/Jamfile defines:
SubDirCcFlags -Wall ;

and the final CFLAGS are:

-Wall -Wno-trigraphs ... -Wall

Since -Wall implies -Wtrigraphs, the final result may be different then expected.