Generate compile_flags.txt for clangd for development

.gitignore

@@ -12,6 +12,7 @@
 /ext/ilios/*.o
 /ext/ilios/mkmf.log
 /ext/ilios/Makefile
+/ext/ilios/compile_flags.txt
 /ext/ilios/cpp-driver
 /ext/ilios/libuv
 /ext/ilios/ports

ext/ilios/extconf.rb

@@ -27,6 +27,22 @@ def num_cpu_cores
   cores >= 7 ? MAX_CORES : cores
 end
 
+def create_compile_flags_txt
+  cppflags = $CPPFLAGS.split(' ')
+  include_flags = cppflags.select { |flag| flag.start_with?('-I') }
+  define_flags = cppflags.select { |flag| flag.start_with?('-D') } + $defs
+
+  File.open('compile_flags.txt', 'w') do |f|
+    include_flags.each { |flag| f.puts(flag) }
+    f.puts "-I#{Dir.pwd}"
+    f.puts "-I#{RbConfig::CONFIG['rubyhdrdir']}"
+    f.puts "-I#{RbConfig::CONFIG['rubyhdrdir']}/ruby/backward"
+    f.puts "-I#{RbConfig::CONFIG['rubyarchhdrdir']}"
+    define_flags.each { |flag| f.puts(flag) }
+  end
+end
+
+
 module LibuvInstaller
   LIBUV_INSTALL_PATH = File.expand_path('libuv')
   private_constant :LIBUV_INSTALL_PATH
@@ -146,3 +162,4 @@ def self.install_from_source
 $LDFLAGS += " #{ENV['LDFLAGS']}"
 
 create_makefile('ilios')
+create_compile_flags_txt