Contrary to other Linux distributions, the glibc library files are not in the
standard ld(1) search path on Guix.  However, cproc only allows us to specify
the gcclibdir.  To workaround that we manually add a feature to cproc's
configure script which allows us to pass extra linkflags via an environment
variable.

diff --git a/configure b/configure
index dab1bf3..a31b456 100755
--- a/configure
+++ b/configure
@@ -159,7 +159,7 @@ static const char *const preprocesscmd[] = {
 $defines};
 static const char *const codegencmd[]    = {"$DEFAULT_QBE"};
 static const char *const assemblecmd[]   = {"$DEFAULT_ASSEMBLER"};
-static const char *const linkcmd[]       = {"$DEFAULT_LINKER", $linkflags};
+static const char *const linkcmd[]       = {"$DEFAULT_LINKER", ${LINKFLAGS_EXTRA:+\"$LINKFLAGS_EXTRA\", }$linkflags};
 EOF
 echo done