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/Makefile

@@ -13,7 +13,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=boost
 PKG_VERSION:=1.71.0
 PKG_SOURCE_VERSION:=1_71_0
-PKG_RELEASE:=4
+PKG_RELEASE:=5
 
 PKG_SOURCE:=$(PKG_NAME)_$(PKG_SOURCE_VERSION).tar.bz2
 PKG_SOURCE_URL:=@SF/$(PKG_NAME)/$(PKG_NAME)/$(PKG_VERSION) https://dl.bintray.com/boostorg/release/$(PKG_VERSION)/source/
@@ -130,7 +130,7 @@ define Package/boost/config
 
 	config boost-fiber-exclude
 		bool
-		default y if (TARGET_ar7 || TARGET_brcm47xx_generic || TARGET_brcm47xx_legacy || TARGET_lantiq_ase || TARGET_rb532 || mips32 || mips64 || boost-coroutine-exclude)
+		default y if boost-coroutine-exclude
 		default n
 
 	menu "Select Boost Options"