build: conditionally build llvm bpf toolchain by default

Unless another toolchain is present (or selected), build the bpf toolchain
whenever a package is selected that needs it.

Signed-off-by: Felix Fietkau <nbd@nbd.name>
(cherry picked from commit 6605e45)

Author: nbd168

include/bpf.mk

@@ -1,4 +1,4 @@
-BPF_DEPENDS := @HAS_BPF_TOOLCHAIN
+BPF_DEPENDS := @HAS_BPF_TOOLCHAIN +@NEED_BPF_TOOLCHAIN
 LLVM_VER:=
 
 CLANG_MIN_VER:=12

package/network/services/unetd/Makefile

@@ -40,6 +40,7 @@ define Package/unetd/config
 		bool "VXLAN support"
 		depends on PACKAGE_unetd
 		depends on HAS_BPF_TOOLCHAIN
+		select NEED_BPF_TOOLCHAIN
 		default y
 
 endef

toolchain/Config.in

@@ -40,9 +40,8 @@ menuconfig TARGET_OPTIONS
 
 	choice BPF_TOOLCHAIN
 		prompt "BPF toolchain" if DEVEL
-		default BPF_TOOLCHAIN_BUILD_LLVM if BUILDBOT
 		default BPF_TOOLCHAIN_PREBUILT if HAS_PREBUILT_LLVM_TOOLCHAIN
-		default BPF_TOOLCHAIN_NONE
+		default BPF_TOOLCHAIN_BUILD_LLVM
 
 		config BPF_TOOLCHAIN_NONE
 			bool "None"
@@ -57,7 +56,7 @@ menuconfig TARGET_OPTIONS
 			bool "Use host LLVM toolchain"
 
 		config BPF_TOOLCHAIN_BUILD_LLVM
-			select USE_LLVM_BUILD
+			select USE_LLVM_BUILD if NEED_BPF_TOOLCHAIN
 			bool "Build LLVM toolchain for eBPF"
 			help
 			  If enabled, a LLVM toolchain for building eBPF binaries will be built.
@@ -320,23 +319,24 @@ config GDB_PYTHON
 	  Enable the python bindings for GDB to allow using python in the gdb shell.
 
 config HAS_BPF_TOOLCHAIN
+	default y if !BPF_TOOLCHAIN_NONE
+	bool
+
+config NEED_BPF_TOOLCHAIN
 	bool
 
 config HAS_PREBUILT_LLVM_TOOLCHAIN
 	def_bool $(shell, [ -f llvm-bpf/.llvm-version ] && echo y || echo n)
 
 config USE_LLVM_HOST
-	select HAS_BPF_TOOLCHAIN
 	bool
 
 config USE_LLVM_PREBUILT
-	select HAS_BPF_TOOLCHAIN
 	default y if !DEVEL && !BUILDBOT && HAS_PREBUILT_LLVM_TOOLCHAIN
 	bool
 
 config USE_LLVM_BUILD
-	default y if !DEVEL && BUILDBOT
-	select HAS_BPF_TOOLCHAIN
+	default y if !DEVEL && NEED_BPF_TOOLCHAIN && (BUILDBOT || !HAS_PREBUILT_LLVM_TOOLCHAIN)
 	bool
 
 config USE_GLIBC