Update how_kernel_compiled.md

`KBUILD_MODULES` is used to decide whether build modules, while `KBUILD_BUILTIN` is for kernel.

Misc/how_kernel_compiled.md

@@ -166,7 +166,7 @@ HOSTCFLAGS   = -Wall -Wmissing-prototypes -Wstrict-prototypes -O2 -fomit-frame-p
 HOSTCXXFLAGS = -O2
 ```
 
-Next we get to the `CC` variable that represents compiler too, so why do we need the `HOST*` variables? `CC` is the target compiler that will be used during kernel compilation, but `HOSTCC` will be used during compilation of the set of the `host` programs (we will see it soon). After this we can see the definition of `KBUILD_MODULES` and `KBUILD_BUILTIN` variables that are used to determine what to compile (kernel, modules or both):
+Next we get to the `CC` variable that represents compiler too, so why do we need the `HOST*` variables? `CC` is the target compiler that will be used during kernel compilation, but `HOSTCC` will be used during compilation of the set of the `host` programs (we will see it soon). After this we can see the definition of `KBUILD_MODULES` and `KBUILD_BUILTIN` variables that are used to determine what to compile (modules, kernel, or both):
 
 ```Makefile
 KBUILD_MODULES :=