build: Drop nonstandard -u flag from copy commands

The cp command is only invoked once, so there is no point in copying only
changed files. Not relying on non-POSIX features of GNU cp allows shedding
some portability indirection.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Use debug llvm in debug qemu-asan build

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Add missing directories to clean target.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Drop unused CLANG_LIB variable.

Also move the CLANG_CC and CLANG_CXX variables down a few lines.

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Place asan CXXFLAGS and LDFLAGS in a variable

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Refactor repetitive llvm configure flags into a variable

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Refactor repetitive klee configure flags into a variable

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Refactor repetitive qemu configure flags into a variable

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Merge llvm, clang and compiler-rt download recipes

Signed-off-by: Diego Biurrun <diego@biurrun.de>
build: Merge clang/llvm/compiler-rt unpack rules.

Signed-off-by: Diego Biurrun <diego@biurrun.de>