build: Auto-compile tests.

With this change, tests run in 46s instead of 230s on my x86_64 laptop
when using ‘guix build -f guix.scm’.

* build-aux/guile.am (.scm.go): Set GUILE_AUTO_COMPILE=0.
* Makefile.am (TESTS_ENVIRONMENT): Set GUILE_AUTO_COMPILE=1 and
XDG_CACHE_HOME.
* guix.scm (guile-fibers)[arguments]: Remove.

Makefile.am

@@ -130,7 +130,14 @@ TESTS += \
 	tests/concurrent-web-server.scm
 endif
 
-TESTS_ENVIRONMENT=top_srcdir="$(abs_top_srcdir)" ./env $(GUILE) -s
+# Tests are calibrated to be compiled (they're much slower when
+# interpreted) so make sure they can be auto-compiled upon 'make
+# check'.
+TESTS_ENVIRONMENT =				\
+  top_srcdir="$(abs_top_srcdir)"		\
+  XDG_CACHE_HOME="$(abs_top_builddir)/tests"	\
+  GUILE_AUTO_COMPILE=1				\
+  "$(top_builddir)/env" $(GUILE) -s
 
 EXTRA_DIST += \
 	$(bin_SCRIPTS) \

build-aux/guile.am

@@ -23,6 +23,6 @@ EXTRA_DIST = $(SOURCES) $(NOCOMP_SOURCES)
 GUILE_WARNINGS = -Wunbound-variable -Warity-mismatch -Wformat
 SUFFIXES = .scm .go
 .scm.go:
-	$(AM_V_GEN) $(top_builddir)/env	\
+	$(AM_V_GEN) GUILE_AUTO_COMPILE=0 $(top_builddir)/env		\
 	  $(GUILE_TOOLS) compile $(GUILE_TARGET) -L "$(abs_top_srcdir)"	\
 	  $(GUILE_WARNINGS) -o "$@" "$<"

guix.scm

@@ -45,14 +45,6 @@
                       "texinfo" "gettext-minimal"))))
     (inputs
      (list (S "guile")))
-    (arguments
-     `(#:phases (modify-phases %standard-phases
-                  (add-before 'configure 'bootstrap
-                    (lambda _
-                      (zero? (system* "./autogen.sh"))))
-                  (add-before 'configure 'setenv
-                    (lambda _
-                      (setenv "GUILE_AUTO_COMPILE" "0"))))))
     (synopsis "Lightweight concurrency facility for Guile")
     (description
      "Fibers is a Guile library that implements a a lightweight concurrency