bmcweb: ignore cast-align error for protobuf headers

Protobuf generated C++ code on 32-bit architectures (e.g., ARMv7-a)
casts `google::protobuf::Message*` (4-byte alignment) to concrete
message types containing 64-bit fields (8-byte alignment requirement)
using `reinterpret_cast`.
Because bmcweb enables `-Wcast-align` and `-Werror`, this causes
compilation errors when building bmcweb targets (e.g., pacemaker)
that include tlbmc protobuf headers on 32-bit platforms.

Append `-Wno-error=cast-align` to CXXFLAGS to prevent these alignment
warnings from failing the build.

Tested:
- platform5: http://fusion2/fbd4f274-0561-31e5-b132-a3fc4365536d
- platform15: http://fusion2/cc372ad5-f7a4-3def-9c11-2828b9a09562
- platform18: http://fusion2/42c37380-6793-3ae1-9166-549b840cfc8b
- platform17: http://fusion2/26070480-54cb-3279-afb8-cf147e9c3051
- platform11+ext: http://fusion2/6794dea6-088e-343b-a45e-c9911e809924
- platform11: http://fusion2/3c008d0c-f51c-3c60-99b1-9caa4604f710
- platform25: http://fusion2/f611d1b8-d45f-32cc-a6b0-fe9b2bf10224
Google-Bug-Id: 481049523
Google-Bug-Id: 482101011
Change-Id: I471fb13673614bffe23e129d4ce18103063b8e1c
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/recipes-phosphor/interfaces/bmcweb_%.bbappend b/recipes-phosphor/interfaces/bmcweb_%.bbappend
index 8a47669..c8734a3 100644
--- a/recipes-phosphor/interfaces/bmcweb_%.bbappend
+++ b/recipes-phosphor/interfaces/bmcweb_%.bbappend
@@ -1,5 +1,7 @@
 require gbmcweb.inc
 
+CXXFLAGS:append = " -Wno-error=cast-align"
+
 FILESEXTRAPATHS:prepend:gbmc := "${THISDIR}/${PN}:"
 
 RDEPENDS:${PN}:append:gbmc = " phosphor-software-manager-updater"