meson: fix coverage build

This moves coverage.h to src/coverage/, and specifies path to coverage.h
with files() directive, to make it can be included even when located
outside of the include directories. Otherwise, libc-wrapper cannot be
built when -Db_coverage=true option is enabled.

Follow-up for 543a48b653.

meson.build

@@ -344,6 +344,7 @@ conf.set10('ENABLE_FIRST_BOOT_FULL_PRESET',                   get_option('first-
 cc = meson.get_compiler('c')
 userspace_c_args = []
 userspace_c_ld_args = []
+userspace_sources = []
 meson_build_sh = find_program('tools/meson-build.sh')
 
 want_tests = get_option('tests')
@@ -1963,9 +1964,7 @@ endif
 
 #####################################################################
 
-if get_option('b_coverage')
-        userspace_c_args += ['-include', 'coverage.h']
-endif
+subdir('src/coverage')
 
 #####################################################################
 
@@ -1980,7 +1979,7 @@ jinja2_cmdline = [meson_render_jinja2, config_h]
 userspace = declare_dependency(
         compile_args : userspace_c_args,
         link_args : userspace_c_ld_args,
-        sources : version_h,
+        sources : userspace_sources,
 )
 
 man_page_depends = []

src/coverage/meson.build

@@ -0,0 +1,6 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+if get_option('b_coverage')
+        userspace_c_args += ['-include', meson.current_source_dir() / 'coverage.h']
+        userspace_sources += files('coverage.h')
+endif

src/version/meson.build

@@ -13,3 +13,4 @@ version_h = custom_target('version',
                 vcs_tag ? '1' : '0',
         ])
 version_include = include_directories('.')
+userspace_sources += [version_h]