[PATCH] meson/mlx5: Suppress -Wunused-value diagnostic

[Sebastian Brzezinka <sebastian.brzezinka@intel.com>]

From: Alexey Marchuk <alexeymar@mellanox.com>

mlx5 common library checks if several symbols/definitions
are presented in system header files. If some are not
presented, they will be enabled by mlx5_glue library.
The problem appears with clang and '-Werror' - code
generated by meson is not compiled due to unused variable:

Code:

        #include <infiniband/mlx5dv.h>
        int main(void) {
            /* If it's not defined as a macro, try to use as a symbol */
            #ifndef mlx5dv_create_flow_action_packet_reformat
                mlx5dv_create_flow_action_packet_reformat;
            #endif
            return 0;
        }
Compiler stdout:

Compiler stderr:
 /hpc/local/work/alexeymar/repo/spdk/dpdk/build-tmp/meson-private/tmp5obnak86/testfile.c:6:17: error: expression result unused [-Werror,-Wunused-value]
                mlx5dv_create_flow_action_packet_reformat;
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

As result, almost all symbols are enabled in mlx5_glue while
they exist is system headers. As result, we get multiple
symbols redefenitions when we compile mlx5_common.
As a solution for this problem we can suppress
-Wunused-vaurable using pragma

DPDK 23.11 note:
Starting with commit bellow, all cflags are passed to the has_header_symbol().
(33d6694) build: use C11 standard
To make sure that the symbol is properly detected, the pedantic flags needs to
be removed.

Signed-off-by: Alexey Marchuk <alexeymar@mellanox.com>
Signed-off-by: Sebastian Brzezinka <sebastian.brzezinka@intel.com>
---
 drivers/common/mlx5/linux/meson.build | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/common/mlx5/linux/meson.build b/drivers/common/mlx5/linux/meson.build
index b3a64547c5..84b2c64041 100644
--- a/drivers/common/mlx5/linux/meson.build
+++ b/drivers/common/mlx5/linux/meson.build
@@ -231,7 +231,11 @@ if  libmtcr_ul_found
 endif
 
 foreach arg:has_sym_args
-    mlx5_config.set(arg[0], cc.has_header_symbol(arg[1], arg[2], dependencies: libs, args: cflags))
+    file_prefix = '#pragma clang diagnostic ignored "-Wunused-value"'
+    cflags += [
+            '-Wno-pedantic',
+    ]
+    mlx5_config.set(arg[0], cc.has_header_symbol(arg[1], arg[2], prefix : file_prefix, dependencies: libs, args: cflags))
 endforeach
 foreach arg:has_member_args
     file_prefix = '#include <' + arg[1] + '>'
-- 
2.34.1

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