toolchain: gcc: update 7.x to 7.3.0

This version still generates broken code in our setup for MIPS.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

toolchain/gcc/patches/7.3.0/850-use_shared_libgcc.patch

@@ -0,0 +1,54 @@
+commit dcfc40358b5a3cae7320c17f8d1cebd5ad5540cd
+Author: Felix Fietkau <nbd@openwrt.org>
+Date:   Sun Feb 12 20:25:47 2012 +0000
+
+    gcc 4.6: port over the missing patch 850-use_shared_libgcc.patch to prevent libgcc crap from leaking into every single binary
+    
+    SVN-Revision: 30486
+--- a/gcc/config/arm/linux-eabi.h
++++ b/gcc/config/arm/linux-eabi.h
+@@ -126,10 +126,6 @@
+   "%{Ofast|ffast-math|funsafe-math-optimizations:crtfastmath.o%s} "	\
+   LINUX_OR_ANDROID_LD (GNU_USER_TARGET_ENDFILE_SPEC, ANDROID_ENDFILE_SPEC)
+ 
+-/* Use the default LIBGCC_SPEC, not the version in linux-elf.h, as we
+-   do not use -lfloat.  */
+-#undef LIBGCC_SPEC
+-
+ /* Clear the instruction cache from `beg' to `end'.  This is
+    implemented in lib1funcs.S, so ensure an error if this definition
+    is used.  */
+--- a/gcc/config/linux.h
++++ b/gcc/config/linux.h
+@@ -53,6 +53,10 @@ see the files COPYING3 and COPYING.RUNTI
+ 	builtin_assert ("system=posix");			\
+     } while (0)
+ 
++#ifndef LIBGCC_SPEC
++#define LIBGCC_SPEC "%{static|static-libgcc:-lgcc}%{!static:%{!static-libgcc:-lgcc_s}}"
++#endif
++
+ /* Determine which dynamic linker to use depending on whether GLIBC or
+    uClibc or Bionic or musl is the default C library and whether
+    -muclibc or -mglibc or -mbionic or -mmusl has been passed to change
+--- a/libgcc/mkmap-symver.awk
++++ b/libgcc/mkmap-symver.awk
+@@ -136,5 +136,5 @@ function output(lib) {
+   else if (inherit[lib])
+     printf("} %s;\n", inherit[lib]);
+   else
+-    printf ("\n  local:\n\t*;\n};\n");
++    printf ("\n\t*;\n};\n");
+ }
+--- a/gcc/config/rs6000/linux.h
++++ b/gcc/config/rs6000/linux.h
+@@ -60,6 +60,9 @@
+ #undef	CPP_OS_DEFAULT_SPEC
+ #define CPP_OS_DEFAULT_SPEC "%(cpp_os_linux)"
+ 
++#undef LIBGCC_SPEC
++#define LIBGCC_SPEC "%{!static:%{!static-libgcc:-lgcc_s}} -lgcc"
++
+ #undef  LINK_SHLIB_SPEC
+ #define LINK_SHLIB_SPEC "%{shared:-shared} %{!shared: %{static:-static}}"
+