[PATCH] toolchain/gcc: set dialects for each version

[Stijn Tintel]

GCC has an option "-std=" to set the language standard for C and C++.
Newer GCC versions sometimes switch to newer standards by default. This
has the potential to break the OpenWrt toolchain build whenever a distro
introduces a new GCC version that uses a newer dialect by default.

Let's set the default dialects used for each of the GCC versions we
support, to avoid these toolchain build failures in the future.

Signed-off-by: Stijn Tintel <stijn at linux-ipv6.be>
---
 toolchain/gcc/common.mk | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/toolchain/gcc/common.mk b/toolchain/gcc/common.mk
index bef4fa37f8..3e31a139cd 100644
--- a/toolchain/gcc/common.mk
+++ b/toolchain/gcc/common.mk
@@ -29,14 +29,20 @@ PKG_SOURCE_URL:=@GNU/gcc/gcc-$(PKG_VERSION)
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION).tar.xz
 
 ifeq ($(PKG_VERSION),8.4.0)
+  C_DIALECT=-std=gnu17
+  CXX_DIALECT=-std=gnu++14
   PKG_HASH:=e30a6e52d10e1f27ed55104ad233c30bd1e99cfb5ff98ab022dc941edd1b2dd4
 endif
 
 ifeq ($(PKG_VERSION),10.3.0)
+  C_DIALECT=-std=gnu17
+  CXX_DIALECT=-std=gnu++14
   PKG_HASH:=64f404c1a650f27fc33da242e1f2df54952e3963a49e06e73f6940f3223ac344
 endif
 
 ifeq ($(PKG_VERSION),11.2.0)
+  C_DIALECT=-std=gnu17
+  CXX_DIALECT=-std=gnu++17
   PKG_HASH:=d08edc536b54c372a1010ff6619dd274c0f1603aa49212ba20f7aa2cda36fa8b
 endif
 
@@ -86,6 +92,8 @@ GCC_CONFIGURE:= \
 		CFLAGS="-O2 -fbracket-depth=512 -pipe" \
 		CXXFLAGS="-O2 -fbracket-depth=512 -pipe" \
 	) \
+	CFLAGS="$(CFLAGS) $(C_DIALECT)" \
+	CXXFLAGS="$(CXXFLAGS) $(CXX_DIALECT)" \
 	$(HOST_SOURCE_DIR)/configure \
 		--with-bugurl=$(BUGURL) \
 		--with-pkgversion="$(PKGVERSION)" \
-- 
2.34.1