CMake: Add a build target for generating a source RPM

[tstellar]

Summary

'make srpm' or 'ninja srpm' will tar up the current source code and then
build a source RPM package.

By default it will use the llvm.spec file to generate the source RPM,
but you can specify your own custom spec file with the
LLVM_SRPM_USER_BINARY_SPECFILE option. CMake will perform variable
substitution on your custom specfile, so you can reference CMake
variables in it. For example:

Version: @LLVM_RPM_SPEC_VERSION@

Note that everything in the source directory will be included in the
tarball so if you have a clang check out in tools/clang, then all
the clang source will end up in the tarball to. It is recommended
to only use this build target with a clean source tree.

[beanz]

LGTM. This is really cool, thanks for putting it together.

CMakeLists.txt

configure_file(
   ${LLVM_INCLUDE_DIR}/llvm/Config/llvm-config.h)
 configure_file(
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Config/abi-breaking.h.cmake
   ${LLVM_INCLUDE_DIR}/llvm/Config/abi-breaking.h)
 configure_file(
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/Support/DataTypes.h.cmake
   ${LLVM_INCLUDE_DIR}/llvm/Support/DataTypes.h)
 
+# Add target for generating source rpm package.
+set(LLVM_SRPM_USER_BINARY_SPECFILE ${CMAKE_CURRENT_SOURCE_DIR}/llvm.spec
+    CACHE FILEPATH ".spec file to use for srpm generation")
+set(LLVM_SRPM_BINARY_SPECFILE ${CMAKE_CURRENT_BINARY_DIR}/llvm.spec)
+set(LLVM_SRPM_DIR "${CMAKE_CURRENT_BINARY_DIR}/srpm")
+
+# SVN_REVISION and GIT_COMMIT get set by the call to add_version_info_from_vcs.
+# DUMMY_VAR contains a version string which we don't care about.
+add_version_info_from_vcs(DUMMY_VAR)
+if ( SVN_REVISION )
+  set(LLVM_RPM_SPEC_REVISION "r${SVN_REVISION}")
+elseif ( GIT_COMMIT )
+  set (LLVM_RPM_SPEC_REVISION "g${GIT_COMMIT}")
+endif()
+
+configure_file(
+  ${LLVM_SRPM_USER_BINARY_SPECFILE}
+  ${LLVM_SRPM_BINARY_SPECFILE} @ONLY)
+
+add_custom_target(srpm
+  COMMAND cpack -G TGZ --config CPackSourceConfig.cmake -B ${LLVM_SRPM_DIR}/SOURCES
+  COMMAND rpmbuild -bs --define '_topdir ${LLVM_SRPM_DIR}' ${LLVM_SRPM_BINARY_SPECFILE})
+
+
 # They are not referenced. See set_output_directory().
 set( CMAKE_RUNTIME_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/bin )
 set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
 set( CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX} )
 
 if(APPLE AND DARWIN_LTO_LIBRARY)
   set(CMAKE_EXE_LINKER_FLAGS
     "${CMAKE_EXE_LINKER_FLAGS} -Wl,-lto_library -Wl,${DARWIN_LTO_LIBRARY}")