disas/libvixl: Protect C system header for C++ compiler

When selecting an ARM target on Debian unstable, we get:

  Compiling C++ object libcommon.fa.p/disas_libvixl_vixl_utils.cc.o
  FAILED: libcommon.fa.p/disas_libvixl_vixl_utils.cc.o
  c++ -Ilibcommon.fa.p -I. -I.. [...] -o libcommon.fa.p/disas_libvixl_vixl_utils.cc.o -c ../disas/libvixl/vixl/utils.cc
  In file included from /home/philmd/qemu/disas/libvixl/vixl/utils.h:30,
                   from ../disas/libvixl/vixl/utils.cc:27:
  /usr/include/string.h:36:43: error: missing binary operator before token "("
     36 | #if defined __cplusplus && (__GNUC_PREREQ (4, 4) \
        |                                           ^
  /usr/include/string.h:53:62: error: missing binary operator before token "("
     53 | #if defined __USE_MISC || defined __USE_XOPEN || __GLIBC_USE (ISOC2X)
        |                                                              ^
  /usr/include/string.h:165:21: error: missing binary operator before token "("
    165 |      || __GLIBC_USE (LIB_EXT2) || __GLIBC_USE (ISOC2X))
        |                     ^
  /usr/include/string.h:174:43: error: missing binary operator before token "("
    174 | #if defined __USE_XOPEN2K8 || __GLIBC_USE (LIB_EXT2) || __GLIBC_USE (ISOC2X)
        |                                           ^
  /usr/include/string.h:492:19: error: missing binary operator before token "("
    492 | #if __GNUC_PREREQ (3,4)
        |                   ^

Relevant information from the host:

  $ lsb_release -d
  Description:    Debian GNU/Linux 11 (bullseye)
  $ gcc --version
  gcc (Debian 10.2.1-6) 10.2.1 20210110
  $ dpkg -S /usr/include/string.h
  libc6-dev: /usr/include/string.h
  $ apt-cache show libc6-dev
  Package: libc6-dev
  Version: 2.31-11

Partially cherry-pick vixl commit 78973f258039f6e96 [*]:

  Refactor VIXL to use `extern` block when including C header
  that do not have a C++ counterpart.

which is similar to commit 875df03b22 ('osdep: protect qemu/osdep.h
with extern "C"').

[*] https://git.linaro.org/arm/vixl.git/commit/?id=78973f258039f6e96

Buglink: https://bugs.launchpad.net/qemu/+bug/1914870
Suggested-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20210516171023.510778-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

disas/libvixl/vixl/code-buffer.h

@@ -27,7 +27,7 @@
 #ifndef VIXL_CODE_BUFFER_H
 #define VIXL_CODE_BUFFER_H
 
-#include <string.h>
+#include <cstring>
 #include "vixl/globals.h"
 
 namespace vixl {

disas/libvixl/vixl/globals.h

@@ -40,15 +40,17 @@
 #define __STDC_FORMAT_MACROS
 #endif
 
-#include <stdint.h>
+extern "C" {
 #include <inttypes.h>
-
-#include <assert.h>
-#include <stdarg.h>
-#include <stdio.h>
 #include <stdint.h>
-#include <stdlib.h>
+}
-#include <stddef.h>
+
+#include <cassert>
+#include <cstdarg>
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+
 #include "vixl/platform.h"
 
 

disas/libvixl/vixl/invalset.h

@@ -27,7 +27,7 @@
 #ifndef VIXL_INVALSET_H_
 #define VIXL_INVALSET_H_
 
-#include <string.h>
+#include <cstring>
 
 #include <algorithm>
 #include <vector>

disas/libvixl/vixl/platform.h

@@ -28,7 +28,9 @@
 #define PLATFORM_H
 
 // Define platform specific functionalities.
+extern "C" {
 #include <signal.h>
+}
 
 namespace vixl {
 inline void HostBreakpoint() { raise(SIGINT); }

disas/libvixl/vixl/utils.cc

@@ -25,7 +25,7 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 #include "vixl/utils.h"
-#include <stdio.h>
+#include <cstdio>
 
 namespace vixl {
 

disas/libvixl/vixl/utils.h

@@ -27,8 +27,8 @@
 #ifndef VIXL_UTILS_H
 #define VIXL_UTILS_H
 
-#include <string.h>
 #include <cmath>
+#include <cstring>
 #include "vixl/globals.h"
 #include "vixl/compiler-intrinsics.h"