Add support for NDK r25

Includes a few tweaks needed to build bpftools with a recent NDK:

- Libcxx prebuilts are no longer included in sources/cxx-stl [1], so
  use the sysroot path instead.
- NDK now defaults to android-legacy.toolchain.cmake [2], irrespective of
  CMake version. With the legacy toolchain some env variables we set such
  as LDFLAGS aren't used, leading to build errors. Force the use of new
  toolchain file and switch to CXXFLAGS as opposed to CMAKE_CXX_FLAGS
  to avoid overriding toolchain defaults [3].

Test: make NDK_PATH=/opt/ndk/android-ndk-r25c bpftools-min

[1] https://android-review.googlesource.com/c/platform/ndk/+/2051541
[2] https://android-review.googlesource.com/c/platform/ndk/+/2064269
[3] android/ndk#1693

projects/bcc/build.mk

@@ -19,10 +19,9 @@ endif
 # generates bcc build files for Android
 $(BCC_ANDROID_BUILD_DIR): $(HOST_OUT_DIR)/bin/flex
 	-mkdir $@
-	cd $@ && LDFLAGS="$(BCC_EXTRA_LDFLAGS)" $(CMAKE) $(BCC_SRCS) \
+	cd $@ && CFLAGS="$(BCC_EXTRA_CFLAGS)" CXXFLAGS="$(BCC_EXTRA_CFLAGS)" LDFLAGS="$(BCC_EXTRA_LDFLAGS)" \
+		$(CMAKE) $(BCC_SRCS) \
 		$(ANDROID_EXTRA_CMAKE_FLAGS) \
-		-DCMAKE_C_FLAGS="$(BCC_EXTRA_CFLAGS)" \
-		-DCMAKE_CXX_FLAGS="$(BCC_EXTRA_CFLAGS)" \
 		-DFLEX_EXECUTABLE=$(abspath $(HOST_OUT_DIR)/bin/flex) \
 		-DBPS_LINK_RT=OFF \
 		-DENABLE_TESTS=OFF \

projects/bpftrace/build.mk

@@ -5,7 +5,6 @@ BPFTRACE_HOST_DEPS = cmake flex
 $(eval $(call project-define,bpftrace))
 
 BPFTRACE_EXTRA_LDFLAGS = "-L$(abspath $(ANDROID_OUT_DIR))/lib"
-BPFTRACE_EXTRA_CFLAGS = "-I$(abspath $(ANDROID_OUT_DIR))/include"
 
 ifeq ($(STATIC_LINKING),true)
 BPFTRACE_EXTRA_CMAKE_FLAGS = -DSTATIC_LINKING=ON
@@ -33,7 +32,6 @@ $(BPFTRACE_ANDROID_BUILD_DIR): $(HOST_OUT_DIR)/bin/flex $(STRIP_THUNK)
 	cd $@ && LDFLAGS="$(BPFTRACE_EXTRA_LDFLAGS)" $(CMAKE) $(BPFTRACE_SRCS) \
 		$(ANDROID_EXTRA_CMAKE_FLAGS) \
 		$(BPFTRACE_EXTRA_CMAKE_FLAGS) \
-		-DCMAKE_C_FLAGS="$(BPFTRACE_EXTRA_CFLAGS)" \
 		-DBUILD_TESTING=OFF \
 		-DENABLE_MAN=OFF \
 		-DFLEX_EXECUTABLE=$(abspath $(HOST_OUT_DIR)/bin/flex) \

toolchain/cmake.mk

@@ -14,6 +14,7 @@ endif
 
 ANDROID_CMAKE_TOOLCHAIN_FILE = $(NDK_PATH)/build/cmake/android.toolchain.cmake
 ANDROID_EXTRA_CMAKE_FLAGS = -DCMAKE_TOOLCHAIN_FILE=$(abspath $(ANDROID_CMAKE_TOOLCHAIN_FILE))
+ANDROID_EXTRA_CMAKE_FLAGS += -DANDROID_USE_LEGACY_TOOLCHAIN_FILE=FALSE
 ANDROID_EXTRA_CMAKE_FLAGS += -DANDROID_ABI=$(CMAKE_ABI)
 ANDROID_EXTRA_CMAKE_FLAGS += -DANDROID_PLATFORM=android-$(NDK_API)
 ANDROID_EXTRA_CMAKE_FLAGS += -DANDROID_STL=c++_shared

toolchain/toolchain.mk

@@ -11,13 +11,10 @@ include toolchain/cmake.mk
 
 ifeq ($(NDK_ARCH), arm64)
 ANDROID_SYSROOT_LIB_SUBDIR = aarch64-linux-android
-LIBCPP_ABI = arm64-v8a
 else ifeq ($(NDK_ARCH), x86_64)
 ANDROID_SYSROOT_LIB_SUBDIR = x86_64-linux-android
-LIBCPP_ABI = x86_64
 else ifeq ($(NDK_ARCH), armv7)
 ANDROID_SYSROOT_LIB_SUBDIR = arm-linux-androideabi
-LIBCPP_ABI = armeabi-v7a
 else
 $(error unknown abi $(NDK_ARCH))
 endif
@@ -30,4 +27,4 @@ ANDROID_SYSROOT_LIB_PATH = \
     $(ANDROID_SYSROOT_PATH)/usr/lib/$(ANDROID_SYSROOT_LIB_SUBDIR)/$(NDK_API)/
 
 $(ANDROID_OUT_DIR)/lib/libc++_shared.so: | $(ANDROID_OUT_DIR)
-	cp $(NDK_PATH)/sources/cxx-stl/llvm-libc++/libs/$(LIBCPP_ABI)/libc++_shared.so $@
+	cp $(ANDROID_SYSROOT_PATH)/usr/lib/$(ANDROID_SYSROOT_LIB_SUBDIR)/libc++_shared.so $@