Simplify kernel config file need.

Don't build a default config file when not needed.

config/kernel_linux.in

@@ -15,15 +15,17 @@ config KERNEL_LINUX_HEADERS_SANITISED
     bool
     prompt "Mazur's sanitized headers (OBSOLETE)"
     depends on OBSOLETE
+    select KERNEL_LINUX_NEEDS_CONFIG
     help
       M. Mazur used to maintain a tree of sanitised headers, but it is now
-      obsoleted by the headers_install rule (above), and has not seen eny
+      obsoleted by the headers_install rule (above), and has not seen any
       update since 2.6.12
 
 config KERNEL_LINUX_HEADERS_COPY
     bool
     prompt "pure kernel headers (REALLY OBSOLETE)"
     depends on OBSOLETE
+    select KERNEL_LINUX_NEEDS_CONFIG
     help
       This will simply copy the kernel headers to the toolchain.
 
@@ -114,9 +116,14 @@ config KERNEL_LINUX_VERBOSE_LEVEL
     default 1 if KERNEL_LINUX_VERBOSITY_1
     default 2 if KERNEL_LINUX_VERBOSITY_2
 
+config KERNEL_LINUX_NEEDS_CONFIG
+    bool
+    default n
+
 config KERNEL_LINUX_CONFIG_FILE
     string
     prompt "Configuration file"
+    depends on KERNEL_LINUX_NEEDS_CONFIG
     default ""
     help
       Path to a kernel configuration file.

scripts/build/kernel_linux.sh

@@ -27,8 +27,13 @@ do_kernel_extract() {
 do_kernel_check_config() {
     CT_DoStep INFO "Checking kernel configuration"
 
-    if [    "${CT_KERNEL_LINUX_HEADERS_USE_CUSTOM_DIR}" != "y" \
-         -a \( -z "${CT_KERNEL_LINUX_CONFIG_FILE}" -o ! -r "${CT_KERNEL_LINUX_CONFIG_FILE}" \) ]; then
+    # Only the copied or sanitised headers need a config file.
+    # Pre-existing headers as well as headers_install don't.
+    if [ "${CT_KERNEL_LINUX_NEEDS_CONFIG}" = "y"        \
+         -a \( -z "${CT_KERNEL_LINUX_CONFIG_FILE}"      \
+               -o ! -r "${CT_KERNEL_LINUX_CONFIG_FILE}" \
+            \)                                          \
+       ]; then
         CT_DoLog WARN "You did not provide a kernel configuration file!"
         CT_DoLog WARN "I will try to generate one for you, but beware!"