Require C++-11

Includes updates to m4/ax_cxx_compile_stdcxx.m4 to make it work with
msvc, which supports C++-11 with no flags but doesn't set __cplusplus
to a recent value.

README.md

@@ -27,9 +27,9 @@ Versions of qpdf prior to version 7 were released under the terms of version 2.0
 
 # Prerequisites
 
-QPDF depends on the external libraries [zlib](http://www.zlib.net/) and [jpeg](http://www.ijg.org/files/). The [libjpeg-turbo](https://libjpeg-turbo.org/) library is also known to work since it is compatible with the regular jpeg library, and QPDF doesn't use any interfaces that aren't present in the straight jpeg8 API. These are part of every Linux distribution and are readily available. Download information appears in the documentation. For Windows, you can download pre-built binary versions of these libraries for some compilers; see [README-windows.md](README-windows.md) for additional details.
+QPDF requires a C++ compiler that supports C++-11.
 
-QPDF requires a C++ compiler that works with STL.  Your compiler must also support `long long`.  Almost all modern compilers do.  If you are trying to port qpdf to a compiler that doesn't support `long long`, you could change all occurrences of `long long` to `long` in the source code, noting that this would break binary compatibility with other builds of qpdf.  Doing so would certainly prevent qpdf from working with files larger than 2 GB, but remaining functionality would most likely work fine.  If you built qpdf this way and it passed its test suite with large file support disabled, you could be confident that you had an otherwise working qpdf.
+QPDF depends on the external libraries [zlib](http://www.zlib.net/) and [jpeg](http://www.ijg.org/files/). The [libjpeg-turbo](https://libjpeg-turbo.org/) library is also known to work since it is compatible with the regular jpeg library, and QPDF doesn't use any interfaces that aren't present in the straight jpeg8 API. These are part of every Linux distribution and are readily available. Download information appears in the documentation. For Windows, you can download pre-built binary versions of these libraries for some compilers; see [README-windows.md](README-windows.md) for additional details.
 
 # Licensing terms of embedded software
 

TODO

@@ -7,18 +7,15 @@ Fuzz Errors
   * Problems inside the jpeg library: 15470, 15751, 18633
   * Timeout: 17630
 
-C++-11 (for qpdf 10)
-====================
-
-* Consider requiring C++-11 for qpdf 10.
-
-* My c++11 branch adds autoconf tests to require C++-11 and
-  re-implements PointerHolder so that it is interchangeable with
-  std::shared_ptr. It is not actually possible to just replace
-  PointerHolder with std::shared_ptr for two reasons: there is no
-  automatic creation of std::shared_ptr<T> from T* like there is for
-  PointerHolder, which breaks some code, and also there is no
-  automatic conversion from something like
+C++-11
+======
+
+* My c++11 branch adds re-implements PointerHolder so that it is
+  interchangeable with std::shared_ptr. It is not actually possible to
+  just replace PointerHolder with std::shared_ptr for two reasons:
+  there is no automatic creation of std::shared_ptr<T> from T* like
+  there is for PointerHolder, which breaks some code, and also there
+  is no automatic conversion from something like
   std::vector<PointerHolder<T>> to std::vector<std::shared_ptr<T>>. It
   may be a good idea to replace PointerHolder with std::shared_ptr in
   the API even if it requires some work for the developer, but even if

aclocal.m4

@@ -12,6 +12,7 @@
 # PARTICULAR PURPOSE.
 
 m4_ifndef([AC_CONFIG_MACRO_DIRS], [m4_defun([_AM_CONFIG_MACRO_DIRS], [])m4_defun([AC_CONFIG_MACRO_DIRS], [_AM_CONFIG_MACRO_DIRS($@)])])
+m4_include([m4/ax_cxx_compile_stdcxx.m4])
 m4_include([m4/ax_random_device.m4])
 m4_include([m4/libtool.m4])
 m4_include([m4/ltoptions.m4])

autofiles.sums

@@ -1,7 +1,7 @@
-098c86e890756ed699b0a31a8a92910bb65c88656b77f6aa986cd644fa7c7ab1  configure.ac
-9c264dc3fac489fd0178d3fa9fd29d5b0ccd37d561e926ef449fa01d99abded7  aclocal.m4
-79ee40c3867f4162a847c005a73a5e388e3882f71dd185d39d9ddf0312133086  libqpdf/qpdf/qpdf-config.h.in
-8c8779c2182b0c4e85d5fc580024601e45b3a2ad95dd00234aaa63d62e491f0c  m4/ax_cxx_compile_stdcxx.m4
+384fa974656199e43cb904500c6013c3c53cb768b26eedb26440305960e07479  configure.ac
+d3f9ee6f6f0846888d9a10fd3dad2e4b1258be84205426cf04d7cef02d61dad7  aclocal.m4
+6bfabf45d5b7cee4160caacc34feed7c36207605c913d973b391ab13f637bc64  libqpdf/qpdf/qpdf-config.h.in
+5297971a0ef90bcd5563eb3f7127a032bb76d3ae2af7258bf13479caf8983a60  m4/ax_cxx_compile_stdcxx.m4
 35bc5c645dc42d47f2daeea06f8f3e767c8a1aee6a35eb2b4854fd2ce66c3413  m4/ax_random_device.m4
 37f8897d5f68d7d484e5457832a8f190ddb7507fa2a467cb7ee2be40a4364643  m4/libtool.m4
 e77ebba8361b36f14b4d0927173a034b98c5d05049697a9ded84d85eb99a7990  m4/ltoptions.m4