install: suppress redundunt warnings with depends_on requirement

When a formula depends on any requirements, they evaluated at most three times:
before locking, before installing dependent, before building formula.
When a non-fatal requirement is specified and thus evaluated three times,
mostly the same warning message is also emitted three times.

This change restricts printing the warning messages only when a bottle is
successfully installed or before building.
Since this timing is after the final dependency computation for each cases,
the warnings will be most useful to check what is not yet satisfied.

Library/Homebrew/formula_installer.rb

@@ -251,6 +251,7 @@ class FormulaInstaller
         opoo "Bottle installation failed: building from source."
         raise BuildToolsError, [formula] unless DevelopmentTools.installed?
       else
+        puts @requirement_messages
         @poured_bottle = true
       end
     end
@@ -260,6 +261,7 @@ class FormulaInstaller
     unless @poured_bottle
       not_pouring = !pour_bottle || @pour_failed
       compute_and_install_dependencies if not_pouring && !ignore_deps?
+      puts @requirement_messages
       build
       clean
 
@@ -334,17 +336,21 @@ class FormulaInstaller
   end
 
   def check_requirements(req_map)
+    @requirement_messages = []
     fatals = []
 
     req_map.each_pair do |dependent, reqs|
       next if dependent.installed?
       reqs.each do |req|
-        puts "#{dependent}: #{req.message}"
+        @requirement_messages << "#{dependent}: #{req.message}"
         fatals << req if req.fatal?
       end
     end
 
-    raise UnsatisfiedRequirements, fatals unless fatals.empty?
+    return if fatals.empty?
+
+    puts @requirement_messages
+    raise UnsatisfiedRequirements, fatals
   end
 
   def install_requirement_default_formula?(req, dependent, build)