mkosi: work-around to make systemd build in Fedora images that lack populated /etc

On Fedora /usr/bin/ld is a symlink managed via the "alternatives"
system. This unfortunately means the binary is not usable in
environments where /var or /etc are unpopulated. Let's address this by
redirecting "ld" to "ld.bfd" manually if such an environment is
detected, via $PATH.

This is useful for building systemd in mkosi with UsrOnly=1 set.

man/systemd-cryptenroll.xml

@@ -215,7 +215,7 @@
 
               <row>
                 <entry>8</entry>
-                <entry><citerefentry><refentrytitle>sd-boot</refentrytitle><manvolnum>8</manvolnum></citerefentry> measures the kernel command line in this PCR.</entry>
+                <entry><citerefentry><refentrytitle>sd-boot</refentrytitle><manvolnum>7</manvolnum></citerefentry> measures the kernel command line in this PCR.</entry>
               </row>
             </tbody>
           </tgroup>

mkosi.build

@@ -14,6 +14,18 @@ if ! mountpoint -q "$SRCDIR"; then
         umask 022
 fi
 
+# On Fedora "ld" is (unfortunately — if you ask me) managed via
+# "alternatives". Since we'd like to support building images in environments
+# with only /usr/ around (e.g. mkosi's UsrOnly=1 option), we have the problem
+# that /usr/bin/ld is a symlink that points to a non-existing file in
+# /etc/alternative/ in this mode. Let's work around this for now by manually
+# redirect "ld" to "ld.bfd", i.e. circumventing the /usr/bin/ld symlink.
+if [ ! -x /usr/bin/ld -a -x /usr/bin/ld.bfd ] ; then
+        mkdir -p "$HOME"/bin
+        ln -s /usr/bin/ld.bfd "$HOME"/bin/ld
+        PATH="$HOME/bin:$PATH"
+fi
+
 # If mkosi.builddir/ exists mkosi will set $BUILDDIR to it, let's then use it
 # as out-of-tree build dir. Otherwise, let's make up our own builddir.
 [ -z "$BUILDDIR" ] && BUILDDIR=build

src/basic/proc-cmdline.c

@@ -47,7 +47,7 @@ static int proc_cmdline_extract_first(const char **p, char **ret_word, ProcCmdli
                 _cleanup_free_ char *word = NULL;
                 const char *c;
 
-                r = extract_first_word(&q, &word, NULL, EXTRACT_UNQUOTE|EXTRACT_RELAX);
+                r = extract_first_word(&q, &word, NULL, EXTRACT_UNQUOTE|EXTRACT_RELAX|EXTRACT_RETAIN_ESCAPE);
                 if (r < 0)
                         return r;
                 if (r == 0)