musl: add s390 support

target/config/Config.in.compiler

@@ -31,6 +31,7 @@ default ADK_TOOLCHAIN_GCC_6 if ADK_TARGET_ARCH_H8300
 default ADK_TOOLCHAIN_GCC_6 if ADK_TARGET_ARCH_FRV
 default ADK_TOOLCHAIN_GCC_6 if ADK_TARGET_ARCH_M32R
 default ADK_TOOLCHAIN_GCC_6 if ADK_TARGET_CPU_MIPS_MIPS32R6 || ADK_TARGET_CPU_MIPS64_MIPS64R6
+default ADK_TOOLCHAIN_GCC_6 if ADK_TARGET_LIB_MUSL && ADK_TARGET_ARCH_S390
 default ADK_TOOLCHAIN_GCC_5
 
 config ADK_TOOLCHAIN_GCC_GIT

target/config/Config.in.libc

@@ -51,6 +51,7 @@ config ADK_TARGET_LIB_MUSL
 		ADK_TARGET_ARCH_OR1K || \
 		ADK_TARGET_ARCH_PPC || \
 		ADK_TARGET_ARCH_PPC64 || \
+		ADK_TARGET_ARCH_S390 || \
 		ADK_TARGET_ARCH_SH || \
 		ADK_TARGET_ARCH_X86 || \
 		ADK_TARGET_ARCH_X86_64 || \

toolchain/gcc/patches/6.2.0/s390-musl.patch

@@ -0,0 +1,15 @@
+diff -Nur gcc-6.2.0.orig/gcc/config/s390/linux.h gcc-6.2.0/gcc/config/s390/linux.h
+--- gcc-6.2.0.orig/gcc/config/s390/linux.h	2016-01-04 15:30:50.000000000 +0100
++++ gcc-6.2.0/gcc/config/s390/linux.h	2016-11-23 00:05:47.186562086 +0100
+@@ -63,6 +63,11 @@
+ #define GLIBC_DYNAMIC_LINKER32 "/lib/ld.so.1"
+ #define GLIBC_DYNAMIC_LINKER64 "/lib/ld64.so.1"
+ 
++#undef MUSL_DYNAMIC_LINKER32
++#define MUSL_DYNAMIC_LINKER32 "/lib/ld-musl-s390.so.1"
++#undef MUSL_DYNAMIC_LINKER64
++#define MUSL_DYNAMIC_LINKER64 "/lib/ld-musl-s390x.so.1"
++
+ #undef  LINK_SPEC
+ #define LINK_SPEC \
+   "%{m31:-m elf_s390}%{m64:-m elf64_s390} \