toolchain: gcc: update 7.x to 7.2.0

Bump gcc from 7.1 to 7.2

Compile & run tested: ar71xx

Trace history of current patches and update with commit ref & comment
to give more clue as to why they're still around/needed.  Some have
changed form since the original commit but some clue is better than no
clue at all.

Signed-off-by: Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk>
Tested-by: Koen Vandeputte <koen.vandeputte@ncentric.com>

toolchain/gcc/patches/7.2.0/230-musl_libssp.patch

@@ -0,0 +1,28 @@
+commit 1877bc9d8f2be143fbe530347a945850d0ecd234
+Author: Steven Barth <cyrus@openwrt.org>
+Date:   Mon Jun 22 10:31:07 2015 +0000
+
+    gcc/musl: rework SSP-support
+    
+    Make musl provide libssp_nonshared.a and make GCC link it unconditionally
+    if musl is used. This should be a no-op if SSP is disabled and seems to be
+    the only reliable way of dealing with SSP over all packages due to the mess
+    that is linkerflags handling in packages.
+    
+    Signed-off-by: Steven Barth <steven@midlink.org>
+    
+    SVN-Revision: 46108
+
+--- a/gcc/gcc.c
++++ b/gcc/gcc.c
+@@ -861,7 +861,9 @@ proper position among the other output f
+ #endif
+ 
+ #ifndef LINK_SSP_SPEC
+-#ifdef TARGET_LIBC_PROVIDES_SSP
++#if DEFAULT_LIBC == LIBC_MUSL
++#define LINK_SSP_SPEC "-lssp_nonshared"
++#elif defined(TARGET_LIBC_PROVIDES_SSP)
+ #define LINK_SSP_SPEC "%{fstack-protector|fstack-protector-all" \
+ 		       "|fstack-protector-strong|fstack-protector-explicit:}"
+ #else