Abseil add_subdirectory fails with weird pkg_config errors

**Describe the bug**



I use Travis CI to build a test suite that uses Abseil. It was working fine before with just doing git clone on the abseil repo and then using it in the project with add_subdirectory and linking the required absl libraries. Recently, a weird issue came up and the travis builds started failing with these errors:

CMake Error: Cannot open file for write: /usr/local/lib/pkgconfig/absl_absl_atomic_hook.pc.tmp

CMake Error: : System Error: No such file or directory

CMake Error: Cannot open file for write: /usr/local/lib/pkgconfig/absl_absl_errno_saver.pc.tmp

CMake Error: : System Error: No such file or directory

CMake Error: Cannot open file for write: /usr/local/lib/pkgconfig/absl_absl_log_severity.pc.tmp



etc. Full log here: https://travis-ci.org/github/askamn/yas/jobs/738220085#L2806



Important point: The test suite builds fine on Windows in Appveyor.



**Steps to reproduce the bug**



The code is available here: https://github.com/askamn/yas/tree/1b3e8bc9f535868897c5789d1548d0f5841a639b

CMakeLists.txt https://github.com/askamn/yas/blob/1b3e8bc9f535868897c5789d1548d0f5841a639b/tests/base/CMakeLists.txt



**What version of Abseil are you using?**



The build step pulled the latest abseil from master.



**What operating system and version are you using**



Ubuntu 14.04.5 LTS



**What compiler and version are you using?**



Fails with both gcc and clang

gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4



**What build system are you using?**



CMake



**Additional context**



Builds fine on windows.

[]