package/proj: fix build failure due to gcc bug 68485(C++)

The proj package exhibits gcc bug 68485 when building for the
Microblaze architecture C files (which was already worked around), but
also for C++ files.

As done for other packages in Buildroot work around this gcc bug by
setting optimization to -O0 when compiling C++ files too if
BR2_TOOLCHAIN_HAS_GCC_BUG_68485=y.

Fixes:
http://autobuild.buildroot.net/results/dc9/dc9bc52ff3d5a83dcfe4a86a391590bef57e1cf0/

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
[Thomas: rework implementation to use a single condition for both CFLAGS and CXXFLAGS]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/proj/proj.mk

@@ -12,11 +12,15 @@ PROJ_INSTALL_STAGING = YES
 PROJ_DEPENDENCIES = host-pkgconf host-sqlite sqlite
 
 PROJ_CFLAGS = $(TARGET_CFLAGS)
+PROJ_CXXFLAGS = $(TARGET_CXXFLAGS)
 
 ifeq ($(BR2_TOOLCHAIN_HAS_GCC_BUG_68485),y)
 PROJ_CFLAGS += -O0
+PROJ_CXXFLAGS += -O0
 endif
 
-PROJ_CONF_ENV = CFLAGS="$(PROJ_CFLAGS)"
+PROJ_CONF_ENV = \
+	CFLAGS="$(PROJ_CFLAGS)" \
+	CXXFLAGS="$(PROJ_CXXFLAGS)"
 
 $(eval $(autotools-package))