Fix autoprofiledbootstrap build

1. Fix gcov version
2. Merge perf data collected when compiling the compiler and runtime libraries
3. Fix documentation typo

Tested on x86_64-pc-linux-gnu.

ChangeLog:

	* Makefile.in: Define PROFILE_MERGER
	* Makefile.tpl: Define PROFILE_MERGER

gcc/c/ChangeLog:

	* Make-lang.in: Merge perf data collected when compiling cc1 and runtime libraries

gcc/cp/ChangeLog:

	* Make-lang.in: Merge perf data collected when compiling cc1plus and runtime libraries

gcc/lto/ChangeLog:

	* Make-lang.in: Merge perf data collected when compiling lto1 and runtime libraries

gcc/ChangeLog:

	* doc/install.texi: Fix documentation typo