Cpreprocessor: adjust line numbers when reading characters from unget-chars-buffer

[masatake]

Fixes #4018.

foo.c

$ cat -n /tmp/foo.c                                                                                                                      
     1	SYSCALL_DEFINE3(
     2	   /*
     3	    * noise
     4	    */
     5	   mysyscall, int, dfd,
     6	   const char __user *, filename,
     7	                umode_t, mode)
     8	{
     9	        return 0
    10	}

With the original code:

$ /usr/bin/ctags --quiet --options=NONE --fields=+Sn -D'SYSCALL_DEFINE3(s,t0,a0,t1,a1,t2,a2)=int s (t0 a0, t1 a1, t2 a2)' -o - /tmp/foo.c
mysyscall	/tmp/foo.c	/^                umode_t, mode)$/;"	f	line:7	typeref:typename:int	signature:(int dfd,const char __user * filename,umode_t mode)

With ctags with this change:

$ ./ctags --quiet --options=NONE --fields=+Sn -D'SYSCALL_DEFINE3(s,t0,a0,t1,a1,t2,a2)=int s (t0 a0, t1 a1, t2 a2)' -o - /tmp/foo.c
mysyscall	/tmp/foo.c	/^   mysyscall, int, dfd,$/;"	f	line:5	typeref:typename:int	signature:(int dfd,const char __user * filename,umode_t mode)

This is a step for solving bootlin/elixir#379.

TODO:

• updating ASM parser, too
• limiting the size of the unget buffer
• updating manual page?

[codecov]

Codecov Report

Attention: Patch coverage is 93.18996% with 19 lines in your changes missing coverage. Please review.

Project coverage is 85.93%. Comparing base (e7db33b) to head (a7a3968).

Files with missing lines	Patch %	Lines
parsers/cpreprocessor.c	91.70%	18 Missing ⚠️
parsers/vera.c	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #4198    +/-   ##
========================================
  Coverage   85.93%   85.93%            
========================================
  Files         241      241            
  Lines       59171    59294   +123     
========================================
+ Hits        50847    50957   +110     
- Misses       8324     8337    +13     

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