Fix build issues with mingw toolchain

With a x86_64-pc-mingw32 toolchain there is a build issue
whether or not the --disable-threading option is used.
The problem happens because _WIN32_WINNT is defined to 0x501
before #include <mutex> which makes the compilation abort
due to missing support for __gthread_cond_t in std_mutex.h,
which is conditional on _WIN32_WINNT >= 0x600.

Fix the case when --disable-threading is used, by only
including <mutex> in gdb/complaints.c when STD_CXX_THREAD
is defined.

Additionally make the configure script try to #include <mutex>
to automatically select --disable-threading when the header file
is not able to compile.

Approved-By: Tom Tromey <tom@tromey.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/gdb/configure b/gdb/configure
index c3d5cf7..98cd488 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -20854,6 +20854,7 @@ else
     # endif
     #endif	/* __MINGW32__ || __CYGWIN__ */
     #include <thread>
+    #include <mutex>
     void callback() { }
 int
 main ()