boost: Fix fiber compilation for mips

The issue was that the pause instruction was emitted through an asm
directive which was not correct for some mips platforms.

Simplified boost-fiber-exclude as a result.

Removed uClibc-ng math patch. It was not correct as it broke float and
long double support (std variants use function overloads). A different
solution was applied upstream. As it's quite annoying to backport, just
wait until a new release comes with that change. ARC as a platform is
barely supported anyways.

Swapped asio patch for the upstream submission, which is unfortunately, in
limbo.

Refreshed remaining patch.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry-picked from f795779c0a)

libs/boost/patches/003-mips-pause.patch

@@ -0,0 +1,28 @@
+From 5f7cda29add367c5381775a314ec9f90e311457a Mon Sep 17 00:00:00 2001
+From: Rosen Penev <rosenp@gmail.com>
+Date: Fri, 15 Nov 2019 12:43:50 -0800
+Subject: [PATCH] cpu_relax: Fix MIPS check
+
+BOOST_ARCH_MIPS as a macro is totally broken. It always gets defined to either 32
+or 64 with a bunch of zeroes depending on the architecture.
+
+Use GCC's internal define to check the architecture properly.
+
+Signed-off-by: Rosen Penev <rosenp@gmail.com>
+---
+ boost/fiber/detail/cpu_relax.hpp | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/boost/fiber/detail/cpu_relax.hpp b/boost/fiber/detail/cpu_relax.hpp
+index 72564394..f40545c2 100644
+--- a/boost/fiber/detail/cpu_relax.hpp
++++ b/boost/fiber/detail/cpu_relax.hpp
+@@ -47,7 +47,7 @@ namespace detail {
+ # else
+ #  define cpu_relax() asm volatile ("nop" ::: "memory");
+ # endif
+-#elif BOOST_ARCH_MIPS
++#elif BOOST_ARCH_MIPS && (__mips_isa_rev > 1)
+ # define cpu_relax() asm volatile ("pause" ::: "memory");
+ #elif BOOST_ARCH_PPC
+ // http://code.metager.de/source/xref/gnu/glibc/sysdeps/powerpc/sys/platform/ppc.h