gcc: disable libsanitizer, libgomp on musl

pkgs/development/compilers/gcc/4.8/default.nix

···
           # To keep ABI compatibility with upstream mingw-w64
           "--enable-fully-dynamic-string"
         ] else
-          optionals (targetPlatform.libc == "uclibc") [
+          optionals (targetPlatform.libc == "uclibc" || targetPlatform.libc == "musl") [
             # In uclibc cases, libgomp needs an additional '-ldl'
             # and as I don't know how to pass it, I disable libgomp.
             "--disable-libgomp"

pkgs/development/compilers/gcc/4.9/default.nix

···
           # To keep ABI compatibility with upstream mingw-w64
           "--enable-fully-dynamic-string"
         ] else
-          optionals (targetPlatform.libc == "uclibc") [
+          optionals (targetPlatform.libc == "uclibc" || targetPlatform.libc == "musl") [
             # libsanitizer requires netrom/netrom.h which is not
             # available in uclibc.
             "--disable-libsanitizer"

pkgs/development/compilers/gcc/5/default.nix

···
           # To keep ABI compatibility with upstream mingw-w64
           "--enable-fully-dynamic-string"
         ] else
-          optionals (targetPlatform.libc == "uclibc") [
+          optionals (targetPlatform.libc == "uclibc" || targetPlatform.libc == "musl") [
             # libsanitizer requires netrom/netrom.h which is not
             # available in uclibc.
             "--disable-libsanitizer"

pkgs/development/compilers/gcc/6/default.nix

···
           # To keep ABI compatibility with upstream mingw-w64
           "--enable-fully-dynamic-string"
         ] else
-          optionals (targetPlatform.libc == "uclibc") [
+          optionals (targetPlatform.libc == "uclibc" || targetPlatform.libc == "musl") [
             # libsanitizer requires netrom/netrom.h which is not
             # available in uclibc.
             "--disable-libsanitizer"
···
       # On Illumos/Solaris GNU as is preferred
       "--with-gnu-as" "--without-gnu-ld"
     ]
+    ++ optional (targetPlatform == hostPlatform && targetPlatform.libc == "musl") "--disable-libsanitizer"
   ;
 
   targetConfig = if targetPlatform != hostPlatform then targetPlatform.config else null;

pkgs/development/compilers/gcc/7/default.nix

···
           # To keep ABI compatibility with upstream mingw-w64
           "--enable-fully-dynamic-string"
         ] else
-          optionals (targetPlatform.libc == "uclibc") [
+          optionals (targetPlatform.libc == "uclibc" || targetPlatform.libc == "musl") [
             # libsanitizer requires netrom/netrom.h which is not
             # available in uclibc.
             "--disable-libsanitizer"