CMake: Update .gitignore for CMake artifacts from in source build.

In source builds are not recommended, but we can make it easier
by ignoring the generated artifacts from CMake.

.gitignore

@@ -5,6 +5,7 @@
 
 .deps
 .libs
+*.a
 *.gcda
 *.gcno
 *.la
@@ -77,3 +78,25 @@ coverage
 /src/liblzma/api/Makefile
 /src/lzmainfo/Makefile
 /src/xzdec/Makefile
+
+/CMakeCache.txt
+/CMakeFiles
+/CTestTestfile.cmake
+/cmake_install.cmake
+/DartConfiguration.tcl
+/liblzma-config-version.cmake
+/liblzma-config.cmake
+/lzcat
+/lzcat.1
+/lzma
+/lzma.1
+/Testing
+/tests_bin/
+/unlzma
+/unlzma.1
+/unxz
+/unxz.1
+/xz
+/xzcat
+/xzcat.1
+/xzdec