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/7.2.0/881-no_tm_section.patch

@@ -0,0 +1,22 @@
+commit 565988ab47bd9b96b50608564aee2104aeb4b7ae
+Author: Felix Fietkau <nbd@nbd.name>
+Date:   Tue Dec 13 14:20:49 2016 +0100
+
+    gcc: rip out transactional memory related bloat from crtbegin
+    
+    Slightly improves compression for each executable, saving about 4k from
+    the default ar71xx rootfs
+    
+    Signed-off-by: Felix Fietkau <nbd@nbd.name>
+
+--- a/libgcc/crtstuff.c
++++ b/libgcc/crtstuff.c
+@@ -152,7 +152,7 @@ call_ ## FUNC (void)					\
+ #endif
+ 
+ #if !defined(USE_TM_CLONE_REGISTRY) && defined(OBJECT_FORMAT_ELF)
+-# define USE_TM_CLONE_REGISTRY 1
++# define USE_TM_CLONE_REGISTRY 0
+ #endif
+ 
+ /* We do not want to add the weak attribute to the declarations of these