Extract crc32 code into a separate static lib

Following what's been suggested on IRC libera.chat #mesonbuild,
this is so that the -march=generic+crc option only applies to
the code it should apply to and not to the entire code base.

meson.build

@@ -40,16 +40,9 @@ elif os == 'gnu' and arch == 'aarch64'
   func_ptr_size = 8
 endif
 
-compiler_opts = []
+global_compiler_opts = []
 if get_option('wrenpp_with_name_guessing')
-  compiler_opts += ['-DWRENPP_WITH_NAME_GUESSING']
+  global_compiler_opts += ['-DWRENPP_WITH_NAME_GUESSING']
-endif
-if get_option('wrenpp_with_sse42')
-  if arch == 'amd64'
-    compiler_opts += ['-msse4.2']
-  elif arch == 'aarch64'
-    compiler_opts += ['-mcpu=generic+crc']
-  endif
 endif
 
 conf.set('POINTER_SIZE', ptr_size)

src/crc32/meson.build

@@ -0,0 +1,24 @@
+compiler_opts = []
+
+if get_option('wrenpp_with_sse42')
+  if arch == 'amd64'
+    compiler_opts += ['-msse4.2']
+  elif arch == 'aarch64'
+    #gcc options here:
+    #https://gcc.gnu.org/onlinedocs/gcc-11.2.0/gcc/AArch64-Options.html
+    compiler_opts += ['-mcpu=generic+crc']
+  endif
+endif
+
+crc32 = static_library('crc32',
+  'crc32.cpp',
+  include_directories: [public_incl, src_incl],
+  install: false,
+  cpp_args: compiler_opts + global_compiler_opts,
+)
+
+crc32_dep = declare_dependency(
+  include_directories: public_incl,
+  link_with: crc32,
+  compile_args: global_compiler_opts,
+)

src/meson.build

@@ -1,3 +1,6 @@
+src_incl = include_directories('.')
+subdir('crc32')
+
 project_config_file = configure_file(
 	input: 'pvt_config.h.in',
 	output: 'pvt_config.h',
@@ -16,17 +19,16 @@ wrenpp = library(meson.project_name(),
   'callback_manager.cpp',
   'class_manager.cpp',
   'wren_class_name_from_type.cpp',
-  'crc32.cpp',
   'module_and_name.cpp',
-  dependencies: [wren_dep],
+  dependencies: [wren_dep, crc32_dep],
   include_directories: public_incl,
   install: (not meson.is_subproject() or get_option('default_library')=='shared'),
-  c_args: compiler_opts,
+  c_args: global_compiler_opts,
-  cpp_args: compiler_opts,
+  cpp_args: global_compiler_opts,
 )
 
 wrenpp_dep = declare_dependency(
   link_with: wrenpp,
   include_directories: public_incl,
-  compile_args: compiler_opts,
+  compile_args: global_compiler_opts,
 )