install kernel headers, synlink /usr/src/linux

a/kernel-gwh/SlackBuild

@@ -31,7 +31,9 @@ fi
 mkdir -p $PKG/usr/src/
 tar xf $CWD/linux-$VERSION.tar.gz -C $PKG/usr/src/
 
-cd $PKG/usr/src/linux-$VERSION
+cd $PKG/usr/src/
+ln -s linux-$VERSION linux
+cd linux-$VERSION
 
 if [ -e $CWD/config-$VERSION ] ; then
     cp $CWD/config-$VERSION .config
@@ -52,6 +54,29 @@ if [[ "$ARCH" == "aarch64" ]]; then
 fi
 make modules_install INSTALL_MOD_PATH=$PKG
 
+if [ -z "${HEADERS_ARCH}" ]; then
+    case "$(uname -m)" in
+    i?86) HEADERS_ARCH=x86 ;;
+    x86_64) HEADERS_ARCH=x86 ;;
+    # Use uname -m for all other archs:
+    *) HEADERS_ARCH=$(uname -m) ;;
+  esac
+fi
+# Generate the kernel headers and clean them up:
+( echo "Generating headers from the Linux kernel source tree in ${KERNEL_SOURCE}:"
+  make headers_install ARCH=${HEADERS_ARCH} INSTALL_HDR_PATH=$PKG/usr
+  cd $PKG/usr/include
+  # You won't want these files. The ones in libdrm work better.
+  rm -rf drm
+  # This next part seems pretty much cosmetic, but since we've been doing this
+  # for a long time (and others also do), we'll stick with it:
+  mv asm asm-${HEADERS_ARCH}
+  ln -sf asm-${HEADERS_ARCH} asm
+  # Remove unneeded dotfiles:
+  find . -name ".??*" -exec rm -f {} \+
+)
+
+
 VERSION=$(basename $(ls $PKG/lib/modules/ | head -n1))
 
 mkdir -p $PKG/install