tools/clang/codesearch: support building with make

Currently, clang tools are built by copying their code into a
llvm-project repository and adding build rule to LLVM's CMake. This
allows pinning a specific LLVM hash which is convenient but it's also a
bit painful to copy code across repositories.

This adds a rule to make that can build syz-codesearch with a simple g++
invocation that uses llvm-config to get the LLVM compiler and linker
flags and hardcodes some clang libraries to link against since I could
not find a better way. (llvm-config does not have "components" for
clang)

Author: FlorentRevest

Makefile

@@ -114,7 +114,7 @@ endif
 	check_copyright check_language check_whitespace check_links check_diff check_commits check_shebang check_html \
 	presubmit presubmit_aux presubmit_build presubmit_arch_linux presubmit_arch_freebsd \
 	presubmit_arch_netbsd presubmit_arch_openbsd presubmit_arch_darwin presubmit_arch_windows \
-	presubmit_arch_executor presubmit_dashboard presubmit_race presubmit_race_dashboard presubmit_old
+	presubmit_arch_executor presubmit_dashboard presubmit_race presubmit_race_dashboard presubmit_old codesearch
 
 all: host target
 host: manager repro mutate prog2c db upgrade
@@ -240,6 +240,15 @@ extract: bin/syz-extract
 bin/syz-extract:
 	GOOS=$(HOSTOS) GOARCH=$(HOSTARCH) $(HOSTGO) build $(GOHOSTFLAGS) -o $@ ./sys/syz-extract
 
+codesearch: bin/syz-codesearch
+
+bin/syz-codesearch: tools/clang/codesearch/codesearch.cpp
+	$(CXX) -Itools/clang $(shell llvm-config --cxxflags) -o $@ $< \
+		-lclangTooling -lclangFrontend -lclangSerialization -lclangDriver \
+		-lclangToolingCore -lclangParse -lclangSema -lclangAPINotes -lclangAnalysis \
+		-lclangASTMatchers -lclangRewrite -lclangEdit -lclangAST -lclangLex -lclangBasic -lclangSupport \
+		$(shell llvm-config --ldflags --libs --system-libs)
+
 # `generate` does *not* depend on any kernel sources, and generates everything
 # in one pass, for all arches. It can be run on a bare syzkaller checkout.
 generate:

tools/clang/codesearch/README.md

@@ -5,4 +5,5 @@ Clang-based tool that indexes kernel source code to power
 agentic tool.
 
 The tool can be built following the procedure described for
-[syz-declextract tool](/tools/syz-declextract/README.md).
+[syz-declextract tool](/tools/syz-declextract/README.md) or with `make
+codesearch`.