rust: remove patch to change path to $S/mk/cfg

Since we no longer use shared source we can modify the source directory
as we build. This drops another patch we need to build and simplifies
the addition of Rust 1.12.1 in #97.

recipes-devtools/rust/rust.inc

@@ -266,6 +266,7 @@ def rust_gen_mk_cfg(d, thing):
     Note that the configure process also depends on the existence of #1, so we
     have to run this before do_configure
     '''
+    import os
     import subprocess
 
     rust_base_sys = rust_base_triple(d, thing)
@@ -275,9 +276,9 @@ def rust_gen_mk_cfg(d, thing):
     llvm_target = d.getVarFlag('LLVM_TARGET', arch, True)
     ldflags = d.getVar('LDFLAGS', True) + d.getVar('HOST_CC_ARCH', True) + d.getVar('TOOLCHAIN_OPTIONS', True)
 
-    b = d.getVar('WORKDIR', True) + '/mk-cfg/'
-    o = open(b + sys_for(d, thing) + '.mk', 'w')
-    i = open(d.getVar('S', True) + '/mk/cfg/' + rust_base_sys + '.mk', 'r')
+    b = os.path.join(d.getVar('S', True), 'mk', 'cfg')
+    o = open(os.path.join(b, sys_for(d, thing) + '.mk'), 'w')
+    i = open(os.path.join(b, rust_base_sys + '.mk'), 'r')
 
     r = subprocess.call(['sed',
         # CFLAGS, LDFLAGS, CXXFLAGS, CPPFLAGS are used by rust's build for a
@@ -335,7 +336,7 @@ python do_rust_arch_fixup () {
         rust_gen_mk_cfg(d, thing)
 }
 addtask rust_arch_fixup before do_configure after do_patch
-do_rust_arch_fixup[dirs] += "${WORKDIR}/mk-cfg"
+do_rust_arch_fixup[dirs] += "${S}/mk/cfg"
 
 llvmdir = "${STAGING_DIR_NATIVE}/${prefix_native}"
 
@@ -374,7 +375,6 @@ do_configure () {
         "--infodir=${infodir}"              \
         "--mandir=${mandir}"                \
         "--libdir=${libdir}"                \
-        "--platform-cfg=${WORKDIR}/mk-cfg/" \
         "--enable-local-rust"               \
         "--local-rust-root=${WORKDIR}/${RUST_SNAPSHOT}/rustc" \
         ${EXTRA_OECONF}