[PATCH 2/2] include, gdb: fix -Wswitch build errors with gcc 4.8

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

I started seeing these strange errors when building with gcc 4.8:

      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)
              ^

It is caused by commit 06de25b7af21 ("gdb: introduce
target_waitkind_str, use it in target_waitstatus::to_string"), which
introduced some pragmas to enable -Wswitch locally.  That shouldn't
affect the rest of the code, since we are using push and pop around
that.  It looks like gcc 4.8 (and 4.9)'s diagnostic push/pop is not
reliable, as it doesn't cause a problem with later versions.

Work around this by not enabling -Wswitch for GCC < 5.  This makes the
code a bit ugly, it would be nice to find a good way to factor this out,
especially if we want to re-use it elsewhere.  But for now, I just want
to un-break the build.

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.  So it shouldn't cause a spurious build error in the
future.  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: I50d66b348bf83de099c3c0879e2eb352d60540ba
---
 gdb/target/waitstatus.c | 9 ++++++++-
 gdb/target/waitstatus.h | 9 ++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/gdb/target/waitstatus.c b/gdb/target/waitstatus.c
index 0fbcec5b7c8..e2388aa80b8 100644
--- a/gdb/target/waitstatus.c
+++ b/gdb/target/waitstatus.c
@@ -29,9 +29,14 @@ target_waitstatus::to_string () const
     ("status->kind = %s", target_waitkind_str (this->kind ()));
 
 /* Make sure the compiler warns if a new TARGET_WAITKIND enumerator is added
-   but not handled here.  */
+   but not handled here.
+
+   GCC 4.8's "diagnostic push/pop" seems broken, it leaves -Werror=switch
+   enabled after the pop.  Skip it for GCC < 5.  */
 DIAGNOSTIC_PUSH
+#if (defined(__GNUC__) && __GNUC__ >= 5) || defined(__clang__)
 DIAGNOSTIC_ERROR_SWITCH
+#endif
   switch (this->kind ())
     {
     case TARGET_WAITKIND_EXITED:
@@ -63,7 +68,9 @@ DIAGNOSTIC_ERROR_SWITCH
     case TARGET_WAITKIND_THREAD_CREATED:
       return str;
     }
+#if (defined(__GNUC__) && __GNUC__ >= 5) || defined(__clang__)
 DIAGNOSTIC_POP
+#endif
 
   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 5b537354184..59014a37362 100644
--- a/gdb/target/waitstatus.h
+++ b/gdb/target/waitstatus.h
@@ -108,9 +108,14 @@ static inline const char *
 target_waitkind_str (target_waitkind kind)
 {
 /* Make sure the compiler warns if a new TARGET_WAITKIND enumerator is added
-   but not handled here.  */
+   but not handled here.
+
+   GCC 4.8's "diagnostic push/pop" seems broken, it leaves -Werror=switch
+   enabled after the pop.  Skip it for GCC < 5.  */
 DIAGNOSTIC_PUSH
+#if (defined(__GNUC__) && __GNUC__ >= 5) || defined(__clang__)
 DIAGNOSTIC_ERROR_SWITCH
+#endif
   switch (kind)
   {
     case TARGET_WAITKIND_EXITED:
@@ -146,7 +151,9 @@ DIAGNOSTIC_ERROR_SWITCH
     case TARGET_WAITKIND_THREAD_EXITED:
       return "THREAD_EXITED";
   };
+#if (defined(__GNUC__) && __GNUC__ >= 5) || defined(__clang__)
 DIAGNOSTIC_POP
+#endif
 
   gdb_assert_not_reached ("invalid target_waitkind value: %d\n", (int) kind);
 }
-- 
2.33.1