test for gcc4 and ban vectors

it has severe code gen problems, it seems

this seems to ban clang as well, unfortunately

ChangeLog

@@ -26,7 +26,7 @@
 
 29/8/17 started 8.5.9
 - make --fail stop jpeg read on any libjpeg warning, thanks @mceachen
-- don't build enumtypes so often, removing perl as a compile dependancy
+- don't build enumtypes so often -- helps remove perl as a compile dependency
 
 2/8/17 started 8.5.8
 - fix transparency detection in merge, thanks Haida
@@ -540,7 +540,7 @@
 - vips_system() now supports many input images and you can change image
   argument order
 - support 16-bit palette TIFFs, plus palette TIFFs can have an alpha
-- libgsf-1 is now an optional dependancy 
+- libgsf-1 is now an optional dependency 
 - dzsave can directly write a ZIP file 
 - add ".vips" as an alternative suffix for vips files
 - added vips_tiffload_buffer()
@@ -1204,9 +1204,9 @@
 - fix gtk-doc warnings
 - small mask load/save improvements
 - mask gtk-doc done
-- add cfitsio dependancy
+- add cfitsio dependency
 - add FITS reader
-- land the vector branch and the orc dependancy ... we have SSE
+- land the vector branch and the orc dependency ... we have SSE
   erode/dilate/add/conv
 - add IM_SWAP
 - dilate/erode do (!=0) on non-uchar images
@@ -2059,7 +2059,7 @@
 - "," allowed as column separator in mask read
 - better at spotting singular matricies
 - small im_render() tidies
-- glib dependancy reduced to just 2.0, but untested ... helps people building
+- glib dependency reduced to just 2.0, but untested ... helps people building
   on older systems who aren't interested in nip2
 - removing leading spaces from IMAGEVEC arguments
 - load non-interlaced PNGs more efficiently

configure.ac

@@ -305,6 +305,29 @@ AC_DEFINE_UNQUOTED(GETTEXT_PACKAGE, "$GETTEXT_PACKAGE",
 ALL_LINGUAS="en_GB de"
 AM_GLIB_GNU_GETTEXT
 
+# we need to disable some features on some known-bad gcc versions
+# these will be "" for clang etc. 
+#
+# I couldn't get this to work, mysterious! do it ourselves
+# 
+# AX_CHECK_COMPILE_FLAG([-dumpversion],
+#   [ax_gcc_version_option=yes],
+#   [ax_gcc_version_option=no]
+# )
+AC_MSG_CHECKING([for gcc version])
+GCC_VERSION=""
+version=$($CC -dumpversion)
+if test $? = 0; then 
+  GCC_VERSION=$version
+  AC_MSG_RESULT([$GCC_VERSION])
+else
+  AC_MSG_RESULT([-dumpversion not supported])
+fi
+
+GCC_VERSION_MAJOR=$(echo $GCC_VERSION | cut -d'.' -f1)
+GCC_VERSION_MINOR=$(echo $GCC_VERSION | cut -d'.' -f2)
+GCC_VERSION_PATCH=$(echo $GCC_VERSION | cut -d'.' -f3)
+
 # Checks for libraries.
 
 # build list of pkg-config packages we used here
@@ -343,6 +366,15 @@ AC_TYPE_MODE_T
 AC_TYPE_OFF_T
 AC_TYPE_SIZE_T
 
+# g++/gcc 4.x have rather broken vector support
+AC_MSG_CHECKING([for gcc with working vector support])
+if test x$GCC_VERSION_MAJOR != x"4"; then
+  AC_MSG_RESULT([yes])
+else
+  ax_cv_have_var_attribute_vector_size=no
+  AC_MSG_RESULT([no])
+fi
+
 # we need to be able to shuffle vectors in C++
 if test x$ax_cv_have_var_attribute_vector_size = x"yes"; then
   AC_MSG_CHECKING([for C++ vector shuffle])