toolchain/gcc: add GCC 8.1.0

Changes compared to GCC 7.x

001-revert_register_mode_search.patch dropped

The underlying issue is described at the end of
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58139

It is fixed by the upstream commit:
3fa2798aa8

020-PR-libstdc-81797-Add-.NOTPARALLEL-to-include-Makefil.patch dropped due to already upstream

100-PR-rtl-optimization-83496.patch dropped due to already upstream

910-mbsd_multi.patch
modified to fix ambiguous overloaded inform() call error

gcc/input.h
header: define UNKNOWN_LOCATION ((source_location) 0)

-        inform (0, "someone does not honour COPTS correctly, passed %d times",
-         honour_copts);
+        inform (UNKNOWN_LOCATION, "someone does not honour COPTS correctly, passed %d times",
+         honour_copts);

940-no-clobber-stamp-bits.patch dropped due to fixed upstream by another way
upstream commit: 87b2d547f8

950-cpp_file_path_translation.patch dropped, Both -fmacro-prefix-map and -ffile-prefix-map are added
to gcc 8.1.0, if I understand it correctly, we should use -fmacro-prefix-map
usage: -fmacro-prefix-map=@var{old}=@var{new}
upstream commit: 859b51f836

-iremap exists as a flag for a long time, for backward compatibility, I think we should keep the
variable name unchanged but change its value in rules.mk for gcc 8.x and higher.

Compile and run tested on x86_64

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

toolchain/gcc/patches/8.1.0/850-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}} \
+   %{static-pie:-static -pie --no-dynamic-linker -z text}"