gdb, gdbserver, gdbsupport: remove -Wno-vla-cxx-extension

Now that all known uses of VLAs within GDB are removed, remove the
`-Wno-vla-cxx-extension` (which was used to silence clang warnings) and
add `-Wvla`, such that any use of a VLA will trigger a warning.

Change-Id: I69a8d7f93f973743165b0ba46f9c2ea8adb89025

gdb/configure

diff --git a/gdb/configure b/gdb/configure
index c3d5cf7..232cdb9 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -31179,7 +31179,7 @@
 -Wredundant-move \
 -Wmissing-declarations \
 -Wstrict-null-sentinel \
--Wno-vla-cxx-extension \
+-Wvla \
 "
 
 # The -Wmissing-prototypes flag will be accepted by GCC, but results

gdbserver/configure

diff --git a/gdbserver/configure b/gdbserver/configure
index 026d250..71d0c2f 100755
--- a/gdbserver/configure
+++ b/gdbserver/configure
@@ -13706,7 +13706,7 @@
 -Wredundant-move \
 -Wmissing-declarations \
 -Wstrict-null-sentinel \
--Wno-vla-cxx-extension \
+-Wvla \
 "
 
 # The -Wmissing-prototypes flag will be accepted by GCC, but results

gdbsupport/configure

diff --git a/gdbsupport/configure b/gdbsupport/configure
index ae99125..bd6fc18 100755
--- a/gdbsupport/configure
+++ b/gdbsupport/configure
@@ -14179,7 +14179,7 @@
 -Wredundant-move \
 -Wmissing-declarations \
 -Wstrict-null-sentinel \
--Wno-vla-cxx-extension \
+-Wvla \
 "
 
 # The -Wmissing-prototypes flag will be accepted by GCC, but results

gdbsupport/warning.m4

diff --git a/gdbsupport/warning.m4 b/gdbsupport/warning.m4
index d12bccb..2dadd7f 100644
--- a/gdbsupport/warning.m4
+++ b/gdbsupport/warning.m4
@@ -52,7 +52,7 @@
 -Wredundant-move \
 -Wmissing-declarations \
 -Wstrict-null-sentinel \
--Wno-vla-cxx-extension \
+-Wvla \
 "
 
 # The -Wmissing-prototypes flag will be accepted by GCC, but results