Disable Valgrind by default during testing (#3269)

Previously, the configure script automatically enables Valgrind during
testing when the valgrind command is found. However, running tests with
Valgrind is quite slow, so it is better to disable it by default, and
to enable it only when the user specifies the `--enable-valgrind` flag.

configure.ac

@@ -39,11 +39,6 @@ if test "$USE_MAINTAINER_MODE" = yes; then
   AC_CHECK_PROGS(LEX, flex lex)
 fi
 
-dnl Check for valgrind
-AC_CHECK_PROGS(valgrind_cmd, valgrind)
-if test "x$valgrind_cmd" = "x" ; then
-    AC_MSG_WARN([valgrind is required to test jq.])
-fi
 AC_CHECK_FUNCS(memmem)
 
 AC_CHECK_HEADER("sys/cygwin.h", [have_cygwin=1;])
@@ -54,10 +49,9 @@ dnl Running tests with Valgrind is slow. It is faster to iterate on
 dnl code without Valgrind until tests pass, then enable Valgrind and
 dnl fix leaks.
 AC_ARG_ENABLE([valgrind],
-   AS_HELP_STRING([--disable-valgrind],[do not run tests under Valgrind]))
+   AS_HELP_STRING([--enable-valgrind],[enable Valgrind during testing]))
 
-dnl Running tests with Valgrind is slow; address sanitizer (ASAN) is
-dnl faster.
+dnl Address sanitizer (ASan)
 AC_ARG_ENABLE([asan],
    AS_HELP_STRING([--enable-asan],[enable address sanitizer]))
 
@@ -114,7 +108,7 @@ AS_IF([test "x$enable_decnum" != "xno"],[
    AC_DEFINE([USE_DECNUM], 1, [Define to enable decnum support.])
 ])
 
-AM_CONDITIONAL([ENABLE_VALGRIND], [test "x$enable_valgrind" != xno])
+AM_CONDITIONAL([ENABLE_VALGRIND], [test "x$enable_valgrind" = xyes])
 AM_CONDITIONAL([ENABLE_ASAN], [test "x$enable_asan" = xyes])
 AM_CONDITIONAL([ENABLE_UBSAN], [test "x$enable_ubsan" = xyes])
 AM_CONDITIONAL([ENABLE_GCOV], [test "x$enable_gcov" = xyes])
@@ -291,7 +285,6 @@ AC_SUBST(onig_LDFLAGS)
 
 AM_CONDITIONAL([BUILD_ONIGURUMA], [test "x$build_oniguruma" = xyes])
 AM_CONDITIONAL([WITH_ONIGURUMA], [test "x$with_oniguruma" != xno])
-AC_SUBST([BUNDLER], ["$bundle_cmd"])
 
 AC_CONFIG_MACRO_DIRS([config/m4 m4])
 AC_CONFIG_HEADERS([src/config.h])