Don't emit generated hip_prof_str.h to source directory

The build should never touch the source directory, and only write
generated files to the output directory.

Also track the dependency with a custom command and target, as is the
normal method for dependencies on generated files.

Change-Id: I9d835256c643aeef241d26ca05ab390ebba65111

.gitignore

@@ -10,7 +10,6 @@ bin/hipInfo
 bin/hipBusBandwidth
 bin/hipDispatchLatency
 bin/hipify-clang
-include/hip/hcc_detail/hip_prof_str.h
 include/hip/hip_version.h
 tags
 samples/1_Utils/hipInfo/hipInfo