tune-core2: Replace -mtune=generic with -mtune=core2

-march specifies which ISA to use. -mtune specifies which cpu-type to
optimize instruction ordering for, but not which ISA to use. There are
times when it may make sense to specify mtune=generic and use a more
specific march, such as core2, but the opposite makes little sense at
all: use cpu-type specific ISA, but order the instructions
generically. While the -mtune is implied by -march, gcc does not verify
it is using -mtune=core2 with:

    gcc -Q -march=core2 --help=target

Explicitly specify -mtune=core2 to be sure.

Add a comment header describing the CPUs targeted by this tune file.

(From OE-Core rev: 4cd33193b2db6c281275db2fb5cc169181955217)

Signed-off-by: Darren Hart <dvhart@linux.intel.com>
Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Cc: Paul Eggleton <paul.eggleton@intel.com>
Cc: Tom Zanussi <tom.zanussi@intel.com>
Cc: Nitin Kamble <nitin.a.kamble@intel.com>
Cc: Mark Hatle <mark.hatle@windriver.com>
Cc: Bruce Ashfield <bruce.ashfield@windriver.com>
Cc: Martin Jansa <martin.jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/conf/machine/include/tune-core2.inc

@@ -1,10 +1,18 @@
+# Settings for the GCC(1) cpu-type "core2":
+#
+#      Intel Core2 CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
+#      instruction set support.
+#
+# This tune is recommended for the Intel Core 2 CPU family, including Conroe,
+# Merom and beyond, as well as the first Atom CPUs, Diamondville, and beyond.
+#
 DEFAULTTUNE ?= "core2"
 
 require conf/machine/include/tune-i586.inc
 
 # Extra tune features
 TUNEVALID[core2] = "Enable core2 specific processor optimizations"
-TUNE_CCARGS .= "${@bb.utils.contains("TUNE_FEATURES", "core2", " -march=core2 -msse3 -mtune=generic -mfpmath=sse", "", d)}"
+TUNE_CCARGS .= "${@bb.utils.contains("TUNE_FEATURES", "core2", " -march=core2 -mtune=core2 -msse3 -mfpmath=sse", "", d)}"
 
 # Extra tune selections
 AVAILTUNES += "core2"