make: Implicit/Search

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1 4.5.5 Directory Search and Implicit Rules
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1 The search through the directories specified in 'VPATH' or with 'vpath'
11 also happens during consideration of implicit rules (⇒Using
 Implicit Rules Implicit Rules.).
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1    For example, when a file 'foo.o' has no explicit rule, 'make'
1 considers implicit rules, such as the built-in rule to compile 'foo.c'
1 if that file exists.  If such a file is lacking in the current
1 directory, the appropriate directories are searched for it.  If 'foo.c'
1 exists (or is mentioned in the makefile) in any of the directories, the
1 implicit rule for C compilation is applied.
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1    The recipes of implicit rules normally use automatic variables as a
1 matter of necessity; consequently they will use the file names found by
1 directory search with no extra effort.
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