Revert "Unexpose config headers (low hanging fruit only) (backport #12773)"

src/libexpr-c/meson.build

@@ -14,6 +14,8 @@ cxx = meson.get_compiler('cpp')
 
 subdir('nix-meson-build-support/deps-lists')
 
+configdata = configuration_data()
+
 deps_private_maybe_subproject = [
   dependency('nix-util'),
   dependency('nix-store'),
@@ -25,6 +27,14 @@ deps_public_maybe_subproject = [
 ]
 subdir('nix-meson-build-support/subprojects')
 
+# TODO rename, because it will conflict with downstream projects
+configdata.set_quoted('PACKAGE_VERSION', meson.project_version())
+
+config_h = configure_file(
+  configuration : configdata,
+  output : 'config-expr.h',
+)
+
 add_project_arguments(
   # TODO(Qyriad): Yes this is how the autoconf+Make system did it.
   # It would be nice for our headers to be idempotent instead.
@@ -34,6 +44,10 @@ add_project_arguments(
   '-include', 'config-store.hh',
   '-include', 'config-expr.hh',
 
+  # From C libraries, for our public, installed headers too
+  '-include', 'config-util.h',
+  '-include', 'config-store.h',
+  '-include', 'config-expr.h',
   language : 'cpp',
 )
 
@@ -47,7 +61,7 @@ sources = files(
 
 include_dirs = [include_directories('.')]
 
-headers = files(
+headers = [config_h] + files(
   'nix_api_expr.h',
   'nix_api_external.h',
   'nix_api_value.h',