[PATCH] configure.ac: turn valgrind automagic into --enable-valgrind option

Hi!

Please consider a patch to configure.ac.

- valgrind headers might be present, but not wished for libreoffice
- if valgrind support is desired but for some reason not found, configure should not keep quiet and 
continue

Attaching a patch that hopes to achieve this in as few lines as possible.

Best regards,
Andreas

--- a/configure.ac      2014-11-01 17:49:19.341284752 +0100
+++ b/configure.ac      2014-11-01 20:04:37.820715480 +0100
@@ -985,6 +985,10 @@
     AS_HELP_STRING([--disable-ooenv],
         [Disable ooenv for the instdir installation.]))
 
+AC_ARG_ENABLE(valgrind,
+    AS_HELP_STRING([--enable-valgrind],
+        [Enable valgrind support.]))
+
 AC_ARG_ENABLE(lto,
     AS_HELP_STRING([--enable-lto],
         [Enable link-time optimization. Suitable for (optimised) product builds. Building might 
take
@@ -5751,10 +5755,12 @@
 AC_SUBST([ENABLE_RUNTIME_OPTIMIZATIONS])
 
 dnl ===================================================================
-dnl Check if valgrind headers are available
+dnl Check whether to enable valgrind support and if headers available
 dnl ===================================================================
 ENABLE_VALGRIND=
-if test "$cross_compiling" != yes; then
+AC_MSG_CHECKING([whether to enable valgrind support])
+if test "$enable_valgrind" = yes -a "$cross_compiling" != yes; then
+    AC_MSG_RESULT([yes])
     prev_cppflags=$CPPFLAGS
     # Is VALGRIND_CFLAGS something one is supposed to have in the environment,
     # or where does it come from?
@@ -5762,6 +5768,11 @@
     AC_CHECK_HEADER([valgrind/valgrind.h],
         [ENABLE_VALGRIND=TRUE])
     CPPFLAGS=$prev_cppflags
+    if test -z "$ENABLE_VALGRIND"; then
+        AC_MSG_ERROR([Could not find valgrind/valgrind.h, but valgrind support was requested.])
+    fi
+else
+    AC_MSG_RESULT([no])
 fi
 AC_SUBST([ENABLE_VALGRIND])
 if test -z "$ENABLE_VALGRIND"; then