gdb, include: replace pragmas with DIAGNOSTIC macros, fix build with g++ 4.8

When introducing this code, I forgot that we had some macros for this.
Replace some "manual" pragma diagnostic with some DIAGNOSTIC_* macros,
provided by include/diagnostics.h.

In diagnostics.h:

 - Add DIAGNOSTIC_ERROR, to enable a diagnostic at error level.
 - Add DIAGNOSTIC_ERROR_SWITCH, to enable -Wswitch at error level, for
   both gcc and clang.

Additionally, using DIAGNOSTIC_PUSH, DIAGNOSTIC_ERROR_SWITCH and
DIAGNOSTIC_POP seems to misbehave with g++ 4.8, where we see these
errors:

      CXX    ada-tasks.o
    /home/smarchi/src/binutils-gdb/gdb/ada-tasks.c: In function void read_known_tasks():
    /home/smarchi/src/binutils-gdb/gdb/ada-tasks.c:998:10: error: enumeration value ADA_TASKS_UNKNOWN not handled in switch [-Werror=switch]
       switch (data->known_tasks_kind)
              ^

Because of the POP, the diagnostic should go back to being disabled,
since it was disabled in the beginning, but that's not what we see
here.  Versions of GCC >= 5 compile correctly.

Work around this by making DIAGNOSTIC_ERROR_SWITCH a no-op for GCC < 5.

Note that this code (already as it exists in master today) enables
-Wswitch at the error level even if --disable-werror is passed.  It
shouldn't be a problem, as it's not like a new enumerator will appear
out of nowhere and cause a build error if building with future
compilers.  Still, for correctness, we would ideally want to ask the
compiler to enable -Wswitch at its default level (as if the user had
passed -Wswitch on the command-line).  There doesn't seem to be a way to
do this.

Change-Id: Id33ebec3de39bd449409ea0bab59831289ffe82d

2 files changed, 7 insertions, 6 deletions

diff --git a/gdb/target/waitstatus.c b/gdb/target/waitstatus.c
index a7209e3f2b7..0fbcec5b7c8 100644
--- a/gdb/target/waitstatus.c
+++ b/gdb/target/waitstatus.c
@@ -30,8 +30,8 @@ target_waitstatus::to_string () const
 
 /* Make sure the compiler warns if a new TARGET_WAITKIND enumerator is added
    but not handled here.  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic error "-Wswitch"
+DIAGNOSTIC_PUSH
+DIAGNOSTIC_ERROR_SWITCH
   switch (this->kind ())
     {
     case TARGET_WAITKIND_EXITED:
@@ -63,7 +63,7 @@ target_waitstatus::to_string () const
     case TARGET_WAITKIND_THREAD_CREATED:
       return str;
     }
-#pragma GCC diagnostic pop
+DIAGNOSTIC_POP
 
   gdb_assert_not_reached ("invalid target_waitkind value: %d",
 			  (int) this->kind ());
diff --git a/gdb/target/waitstatus.h b/gdb/target/waitstatus.h
index 48405d222f4..5b537354184 100644
--- a/gdb/target/waitstatus.h
+++ b/gdb/target/waitstatus.h
@@ -20,6 +20,7 @@
 #ifndef TARGET_WAITSTATUS_H
 #define TARGET_WAITSTATUS_H
 
+#include "diagnostics.h"
 #include "gdbsupport/gdb_signals.h"
 
 /* Stuff for target_wait.  */
@@ -108,8 +109,8 @@ target_waitkind_str (target_waitkind kind)
 {
 /* Make sure the compiler warns if a new TARGET_WAITKIND enumerator is added
    but not handled here.  */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic error "-Wswitch"
+DIAGNOSTIC_PUSH
+DIAGNOSTIC_ERROR_SWITCH
   switch (kind)
   {
     case TARGET_WAITKIND_EXITED:
@@ -145,7 +146,7 @@ target_waitkind_str (target_waitkind kind)
     case TARGET_WAITKIND_THREAD_EXITED:
       return "THREAD_EXITED";
   };
-#pragma GCC diagnostic pop
+DIAGNOSTIC_POP
 
   gdb_assert_not_reached ("invalid target_waitkind value: %d\n", (int) kind);
 }