buildgcc: Don't request that optional tools be installed

Previously, when we tested for g++ and two different versions of clang,
if the earlier versions were not found, buildgcc would still request
that they be installed.  This obviously isn't needed, and isn't the
desired outcome.
Now, if one of the first tests fails, nothing gets printed.  If all
the tests fail, it tells you to install either g++ or clang.

Change-Id: I71359f59c4c6bee3c3c55e4e6105f11e6ca51527
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12852
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/crossgcc/buildgcc

@@ -114,6 +114,9 @@ please_install()
 	esac
 
 	printf "${RED}ERROR:${red} Missing tool: Please install \'$1\' utility. (eg $solution)${NC}\n" >&2
+	if [ -n "$2" ]; then
+		printf "${RED}ERROR:${red}               or install \'$2\' utility. (eg $solution)${NC}\n" >&2
+	fi
 }
 
 searchtool()
@@ -121,6 +124,7 @@ searchtool()
 	# $1 short name
 	# $2 search string
 	# $3 soft fail if set
+	# $4 alternative package to install on failure
 	# result: file name of that tool on stdout
 	#         or no output if nothing suitable was found
 	search=GNU
@@ -166,8 +170,8 @@ searchtool()
 			fi
 		fi
 	fi
-	please_install $1
+
-	[ -z "$3" ] && exit 1
+	[ -z "$3" ] && please_install $1 $4 && exit 1
 	false
 }
 
@@ -643,7 +647,7 @@ searchtool bison > /dev/null
 searchtool flex flex > /dev/null
 searchtool g++ "Free Software Foundation" nofail > /dev/null || \
 searchtool clang "clang version" nofail > /dev/null || \
-searchtool clang "LLVM"  > /dev/null
+searchtool clang "LLVM" "" "g++" > /dev/null
 searchtool wget > /dev/null
 searchtool bzip2 "bzip2," > /dev/null