Make test scripts check GUILE environment variable

So that they use the guile (or guile.exe, in the MinGW case) that was
just built, and not just any guile that can be found in the PATH.

* test-suite/standalone/test-asmobs: Use ${GUILE:-guile} instead of
  guile.

* test-suite/standalone/test-bad-identifiers: Ditto.

* test-suite/standalone/test-fast-slot-ref.in: Ditto.

* test-suite/standalone/test-require-extension: Ditto.

* test-suite/standalone/test-system-cmds: Ditto.

* test-suite/standalone/test-use-srfi.in: Ditto.

test-suite/standalone/test-asmobs

@@ -1,5 +1,5 @@
 #!/bin/sh
-exec guile -q -s "$0" "$@"
+exec ${GUILE:-guile} -q -s "$0" "$@"
 !#
 
 (load-extension (string-append (getenv "builddir") "/libtest-asmobs")

test-suite/standalone/test-bad-identifiers

@@ -1,5 +1,5 @@
 #!/bin/sh
-exec guile -q -s "$0" "$@"
+exec ${GUILE:-guile} -q -s "$0" "$@"
 !#
 
 ;; The use of certain identifiers as variable or parameter names has

test-suite/standalone/test-fast-slot-ref.in

@@ -25,7 +25,7 @@
 # executing the (%fast-slot-ref i 3) line.  For reasons as yet
 # unknown, it does not cause a segmentation fault if the same code is
 # loaded as a script; that is why we run it here using "guile -q <<EOF".
-exec guile -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm >/dev/null 2>&1 <<EOF
+exec ${GUILE:-guile} -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm >/dev/null 2>&1 <<EOF
 (use-modules (oop goops))
 (define-module (oop goops))
 (define-class <c> () (a #:init-value 1) (b #:init-value 2) (c #:init-value 3))

test-suite/standalone/test-require-extension

@@ -7,12 +7,12 @@ set -e
 # (Note the syntax "! guile -c ..." isn't used here, because that doesn't
 # work on Solaris 10.)
 #
-guile -q -c '(require-extension 7)' 2>/dev/null            && exit 1
-guile -q -c '(require-extension (blarg))' 2>/dev/null      && exit 1
-guile -q -c '(require-extension (srfi "foo"))' 2>/dev/null && exit 1
+${GUILE:-guile} -q -c '(require-extension 7)' 2>/dev/null            && exit 1
+${GUILE:-guile} -q -c '(require-extension (blarg))' 2>/dev/null      && exit 1
+${GUILE:-guile} -q -c '(require-extension (srfi "foo"))' 2>/dev/null && exit 1
 
 # expect these to succeed
-guile -q -c '(require-extension (srfi 1)) (exit (procedure? take-right))'
-guile -q -c '(require-extension (srfi))'
+${GUILE:-guile} -q -c '(require-extension (srfi 1)) (exit (procedure? take-right))'
+${GUILE:-guile} -q -c '(require-extension (srfi))'
 
 exit 0

test-suite/standalone/test-system-cmds

@@ -1,5 +1,5 @@
 #!/bin/sh
-exec guile -q -s "$0" "$@"
+exec ${GUILE:-guile} -q -s "$0" "$@"
 !#
 
 (define (test-system-cmd)

test-suite/standalone/test-use-srfi.in

@@ -19,7 +19,7 @@
 
 # Test that two srfi numbers on the command line work.
 #
-guile -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm --use-srfi=1,10 >/dev/null <<EOF
+${GUILE:-guile} -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm --use-srfi=1,10 >/dev/null <<EOF
 (if (and (defined? 'partition)
          (defined? 'define-reader-ctor))
     (exit 0)   ;; good
@@ -38,7 +38,7 @@ fi
 # `top-repl' the core bindings got ahead of anything --use-srfi gave.
 #
 
-guile -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm --use-srfi=1 >/dev/null <<EOF
+${GUILE:-guile} -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm --use-srfi=1 >/dev/null <<EOF
 (catch #t
   (lambda ()
     (iota 2 3 4))
@@ -56,7 +56,7 @@ fi
 # exercises duplicates handling in `top-repl' versus `use-srfis' (in
 # boot-9.scm).
 #
-guile -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm --use-srfi=17 >/dev/null <<EOF
+${GUILE:-guile} -q -l @top_builddir_absolute@/libguile/stack-limit-calibration.scm --use-srfi=17 >/dev/null <<EOF
 (if (procedure-with-setter? car)
     (exit 0)   ;; good
     (exit 1))  ;; bad