gn-utils.inc: use target variables without TARGET_ prefix

* CXXFLAGS compared with TARGET_CXXFLAGS have few more options
  meta/conf/distro/include/tclibc-glibc.inc appends
    -fvisibility-inlines-hidden
  meta-clang/classes/clang.bbclass appends
    ${LIBCPLUSPLUS}

* we can use this instead of adding LIBCPLUSPLUS to TUNE_CCARGS in
  #554

* instead of ${TARGET_PREFIX}readelf use READELF variable from bitbake.conf:
  it uses HOST_PREFIX which is better and is available since morty with:
  https://git.openembedded.org/openembedded-core/commit/?id=3442ee423813d547be7899a25ea31efe719e662f

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

Author: shr-project

meta-chromium/recipes-browser/chromium/chromium.inc

@@ -34,10 +34,6 @@ RUNTIME = "llvm"
 # This also ensures that it does not rely too much on meta-clang's defaults.
 LIBCPLUSPLUS = "-stdlib=libc++"
 
-# LIBCPLUSPLUS is included in CXXFLAGS and LDFLAGS, but chromium doesn't respect it
-# add it to TUNE_CCARGS as well to include it in CC/CXX variables which are respected.
-TUNE_CCARGS += "${LIBCPLUSPLUS}"
-
 inherit mime-xdg pythonnative
 DEPENDS += "python-setuptools-native"
 

meta-chromium/recipes-browser/chromium/gn-utils.inc

@@ -93,11 +93,11 @@ def write_toolchain_file(d, file_path):
         'cxx': d.expand('${CXX}'),
         'ar': d.expand('${AR}'),
         'nm': d.expand('${NM}'),
-        'readelf': d.expand('${TARGET_PREFIX}readelf'),
-        'extra_cflags': d.expand('${TARGET_CFLAGS}'),
-        'extra_cppflags': d.expand('${TARGET_CPPFLAGS}'),
-        'extra_cxxflags': d.expand('${TARGET_CXXFLAGS}'),
-        'extra_ldflags': d.expand('${TARGET_LDFLAGS}'),
+        'readelf': d.expand('${READELF}'),
+        'extra_cflags': d.expand('${CFLAGS}'),
+        'extra_cppflags': d.expand('${CPPFLAGS}'),
+        'extra_cxxflags': d.expand('${CXXFLAGS}'),
+        'extra_ldflags': d.expand('${LDFLAGS}'),
     }
 
     with open(file_path, 'w') as toolchain_file: