build: fix parallel builds of applications

When building with more than 1 job, we were getting:

make[1]: warning: jobserver unavailable: using -j1.  Add '+' to parent make rule.

Trying to fix this in the Makefile resulted in dependency issues and unsatisfied
dependencies in the compilation and build chain.

Change-Id: Ic73d089cf6a0a0d7b6fd83908b8144c34af25582
Signed-off-by: Anas Nashif <anas.nashif@intel.com>

Makefile

@@ -761,12 +761,12 @@ quiet_cmd_create-lnk = LINK    $@
 $(KERNEL_NAME).lnk:
 	$(call cmd,create-lnk)
 
-linker.cmd:
+linker.cmd: $(zephyr-deps)
 	$(Q)$(CC) -x assembler-with-cpp -nostdinc -undef -E -P \
 	$(LDFLAG_LINKERCMD) $(LD_TOOLCHAIN) -I$(srctree)/include \
 	-I$(objtree)/include/generated $(KBUILD_LDS) -o $@
 
-final-linker.cmd:
+final-linker.cmd: $(zephyr-deps)
 	$(Q)$(CC) -x assembler-with-cpp -nostdinc -undef -E -P \
 	$(LDFLAG_LINKERCMD) $(LD_TOOLCHAIN) -DFINAL_LINK -I$(srctree)/include \
 	-I$(objtree)/include/generated $(KBUILD_LDS) -o $@

Makefile.inc

@@ -52,7 +52,7 @@ else
   S = -s
 endif
 
-zephyrmake	= @$(MAKE) -C $(ZEPHYR_BASE)  O=$(1) CFLAGS=$(CFLAGS) \
+zephyrmake	= @+$(MAKE) -C $(ZEPHYR_BASE)  O=$(1) CFLAGS=$(CFLAGS) \
 			PROJECT=$(PROJECT_BASE) SOURCE_DIR=$(SOURCE_DIR) $(2)
 
 DOTCONFIG = $(O)/.config