Bug 1822462 - Use TARGET_C{,XX}FLAGS consistently between platforms. …

…r=firefox-build-system-reviewers,andi

In some cases, TARGET_CC/TARGET_CXX are ignored by build scripts.
For consistency, also use TARGET_CFLAGS/TARGET_CXXFLAGS for Linux.

Differential Revision: https://phabricator.services.mozilla.com/D172646

taskcluster/scripts/misc/build-rust-based-toolchain.sh

@@ -17,8 +17,8 @@ x86_64-unknown-linux-gnu)
     export RUSTFLAGS="-Clinker=$MOZ_FETCHES_DIR/clang/bin/clang++ -C link-arg=--sysroot=$MOZ_FETCHES_DIR/sysroot-x86_64-linux-gnu -C link-arg=-fuse-ld=lld"
     export CC=$MOZ_FETCHES_DIR/clang/bin/clang
     export CXX=$MOZ_FETCHES_DIR/clang/bin/clang++
-    export CFLAGS="--sysroot=$MOZ_FETCHES_DIR/sysroot-x86_64-linux-gnu"
-    export CXXFLAGS="-D_GLIBCXX_USE_CXX11_ABI=0 --sysroot=$MOZ_FETCHES_DIR/sysroot-x86_64-linux-gnu"
+    export TARGET_CFLAGS="--sysroot=$MOZ_FETCHES_DIR/sysroot-x86_64-linux-gnu"
+    export TARGET_CXXFLAGS="-D_GLIBCXX_USE_CXX11_ABI=0 --sysroot=$MOZ_FETCHES_DIR/sysroot-x86_64-linux-gnu"
     ;;
 *-apple-darwin)
     # Cross-compiling for Mac on Linux.
@@ -31,8 +31,8 @@ x86_64-unknown-linux-gnu)
     fi
     export CC="$MOZ_FETCHES_DIR/clang/bin/clang"
     export CXX="$MOZ_FETCHES_DIR/clang/bin/clang++"
-    export TARGET_CC="$CC -isysroot $MOZ_FETCHES_DIR/MacOSX13.0.sdk"
-    export TARGET_CXX="$CXX -isysroot $MOZ_FETCHES_DIR/MacOSX13.0.sdk -stdlib=libc++"
+    export TARGET_CFLAGS="-isysroot $MOZ_FETCHES_DIR/MacOSX13.0.sdk"
+    export TARGET_CXXFLAGS="-isysroot $MOZ_FETCHES_DIR/MacOSX13.0.sdk -stdlib=libc++"
     ;;
 *-pc-windows-msvc)
     # Cross-compiling for Windows on Linux.