Add compiler target compile options.

For clang, this allows passing -target <triple> to the compiler, and
for qcc, -V<arch> using toolchain files containing something like

 set(triple arm-linux-gnueabihf)
 set(CMAKE_C_COMPILER "/usr/bin/clang")
 set(CMAKE_C_COMPILER_TARGET ${triple})
 set(CMAKE_CXX_COMPILER "/usr/bin/clang++")
 set(CMAKE_CXX_COMPILER_TARGET ${triple})

or

 set(arch gcc_ntoarmv7le)
 set(CMAKE_C_COMPILER /opt/qnx650/host/linux/x86/usr/bin/qcc)
 set(CMAKE_C_COMPILER_TARGET ${arch})
 set(CMAKE_CXX_COMPILER /opt/qnx650/host/linux/x86/usr/bin/QCC)
 set(CMAKE_CXX_COMPILER_TARGET ${arch})

Both clang and qcc are inherently cross compiler( driver)s.

When cross-compiling with clang, use the CMAKE_${lang}_COMPILER_TARGET
as the _CMAKE_TOOLCHAIN_PREFIX to find the appropriate binutils.

When cross-compiling with QNX qcc, use the CMAKE_${lang}_COMPILER_TARGET
to set the appropriate _CMAKE_TOOLCHAIN_PREFIX.

1 files changed, 11 insertions, 0 deletions

diff --git a/Help/variable/CMAKE_LANG_COMPILER_TARGET.rst b/Help/variable/CMAKE_LANG_COMPILER_TARGET.rst
new file mode 100644
index 0000000..7c8efee
--- /dev/null
+++ b/Help/variable/CMAKE_LANG_COMPILER_TARGET.rst
@@ -0,0 +1,11 @@
+CMAKE_<LANG>_COMPILER_TARGET
+----------------------------
+
+The target for cross-compiling, if supported.
+
+Some compiler drivers are inherently cross-compilers, such as clang and
+QNX qcc. These compiler drivers support a command-line argument to specify
+the target to cross-compile for.
+
+This variable may only be set in a toolchain file specified by
+the ``CMAKE_TOOLCHAIN_FILE`` variable.