build: subsystem shared libraries need to depend on crti.o
build: checkBuildSystem.pl now downloads NASM for x86_64-pedigree
build: get compiler target and version in SCons environment variables
build: fix safeAppend to properly avoid duplicating flags
build: use DWARF2 instead of stabs for debug information, as stabs are useless for x86_64
build: use SCons environment compiler version and target to find C++ includes, rather than hardcoding the values.
build: fix SDL app build dependencies (depends on libui)
core: small code fixups found when compiling for x86_64