tree-wide: check if necessary cflags dependencies are set

This makes each `foo_cflags` dependency define a `SYSTEMD_CFLAGS_MARKER_FOO`
macro, and checks if the macro is set when headers provided by external
libraries are included.

With this, we can fail fast at compile time if necessary `_cflags`
dependencies are omitted in meson.build. Missing dependencies found by this
mechanism have been added across the tree.

src/cryptsetup/cryptsetup-tokens/meson.build

@@ -5,7 +5,10 @@ lib_cryptsetup_token_common = static_library(
         'cryptsetup-token-util.c',
         include_directories : includes,
         implicit_include_directories : false,
-        dependencies : userspace,
+        dependencies : [
+                libcryptsetup_cflags,
+                userspace,
+        ],
         link_with : libshared,
         build_by_default : false)
 

src/cryptsetup/meson.build

@@ -23,11 +23,15 @@ executables += [
                         libmount_cflags,
                         libopenssl_cflags,
                         libp11kit_cflags,
+                        tpm2_cflags,
                 ],
         },
         generator_template + {
                 'name' : 'systemd-cryptsetup-generator',
                 'sources' : files('cryptsetup-generator.c'),
+                'dependencies' : [
+                        libcryptsetup_cflags,
+                ],
         },
 ]