classes: Add a mechanism, to select components to be able to select default compiler

We add clang as an alternative compiler, it sitll uses underlying
binutils and compiler runtime, it will only do the compilation and defer
link, to GNU ld/gold, to compile a component usign clang add

TOOLCHAIN_pn-<recipe-name> = "clang"
DEPENDS_append_pn-<recipe-name> = " clang-cross "

And OE will start using clang to compile <recipe-name>

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

3 files changed, 25 insertions, 0 deletions

diff --git a/classes/clang.bbclass b/classes/clang.bbclass
new file mode 100644
index 0000000..f6cb648
--- /dev/null
+++ b/classes/clang.bbclass
@@ -0,0 +1,10 @@
+
+# Add the necessary override
+TOOLCHAINOVERRIDES = ":toolchain-${TOOLCHAIN}"
+TOOLCHAINOVERRIDES[vardepsexclude] = "TOOLCHAIN"
+
+OVERRIDES .= "${TOOLCHAINOVERRIDES}"
+OVERRIDES[vardepsexclude] += "TOOLCHAINOVERRIDES"
+
+require conf/clang.conf
+
diff --git a/conf/clang.conf b/conf/clang.conf
new file mode 100644
index 0000000..8565721
--- /dev/null
+++ b/conf/clang.conf
@@ -0,0 +1,9 @@
+TOOLCHAIN ?= ""
+
+CC_toolchain-clang  = "${TARGET_PREFIX}clang ${TOOLCHAIN_OPTIONS}"
+CXX_toolchain-clang = "${TARGET_PREFIX}clang++ ${TOOLCHAIN_OPTIONS}"
+CPP_toolchain-clang = "${TARGET_PREFIX}clang ${TOOLCHAIN_OPTIONS} -E"
+CCLD_toolchain-clang = "${TARGET_PREFIX}clang ${TOOLCHAIN_OPTIONS}"
+
+TOOLCHAIN_pn-lzo = "clang"
+DEPENDS_append_pn-lzo = " clang-cross "
diff --git a/conf/layer.conf b/conf/layer.conf
index 91c6ff0..ec86d64 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -7,3 +7,9 @@ BBFILES += "${LAYERDIR}/recipes*/*/*.bb ${LAYERDIR}/recipes*/*/*.bbappend"
 BBFILE_COLLECTIONS += "clang-layer"
 BBFILE_PATTERN_clang-layer := "^${LAYERDIR}/"
 BBFILE_PRIORITY_clang-layer = "7"
+
+#PREFERRED_PROVIDER_gcc-cross-initial-${TARGET_ARCH}_forcevariable = "clang-cross"
+#PREFERRED_PROVIDER_virtual/${TARGET_PREFIX}gcc-initial_forcevariable = "clang-cross"
+PREFERRED_PROVIDER_libgcc-initial = "libgcc-initial"
+
+INHERIT += "clang"