tsan: remove duplicate arch switch in buildgo.sh

[dvyukov]

Summary

For some reason we have 2 switches on arch and add
half of arch flags in one place and half in another.
Merge these 2 switches.

compiler-rt/lib/tsan/go/buildgo.sh

SRCS="
     ../../sanitizer_common/sanitizer_procmaps_linux.cpp
     ../../sanitizer_common/sanitizer_linux.cpp
     ../../sanitizer_common/sanitizer_linux_libcdep.cpp
     ../../sanitizer_common/sanitizer_stoptheworld_linux_libcdep.cpp
     ../../sanitizer_common/sanitizer_stoptheworld_netbsd_libcdep.cpp
     "
   if [ "`uname -a | grep ppc64le`" != "" ]; then
     SUFFIX="linux_ppc64le"
-    ARCHCFLAGS="-m64"
+    ARCHCFLAGS="-m64 -mcpu=power8 -fno-function-sections"
   elif [ "`uname -a | grep x86_64`" != "" ]; then
     SUFFIX="linux_amd64"
-    ARCHCFLAGS="-m64"
+    ARCHCFLAGS="-m64 -msse3"
     OSCFLAGS="$OSCFLAGS -ffreestanding -Wno-unused-const-variable -Werror -Wno-unknown-warning-option"
   elif [ "`uname -a | grep aarch64`" != "" ]; then
     SUFFIX="linux_arm64"
     ARCHCFLAGS=""
   elif [ "`uname -a | grep -i mips64`" != "" ]; then
     if [ "`lscpu | grep -i Little`" != "" ]; then
       SUFFIX="linux_mips64le"
       ARCHCFLAGS="-mips64 -EL"

 rm -f $DIR/gotsan.cpp
 for F in $SRCS; do
   cat $F >> $DIR/gotsan.cpp
 done
 
 FLAGS=" -I../rtl -I../.. -I../../sanitizer_common -I../../../include -std=c++14 -Wall -fno-exceptions -fno-rtti -DSANITIZER_GO=1 -DSANITIZER_DEADLOCK_DETECTOR_VERSION=2 $OSCFLAGS $ARCHCFLAGS $EXTRA_CFLAGS"
 DEBUG_FLAGS="$FLAGS -DSANITIZER_DEBUG=1 -g"
 FLAGS="$FLAGS -DSANITIZER_DEBUG=0 -O3 -fomit-frame-pointer"
-if [ "$SUFFIX" = "linux_ppc64le" ]; then
-  FLAGS="$FLAGS -mcpu=power8 -fno-function-sections"
-elif [ "$SUFFIX" = "linux_amd64" ]; then
-  FLAGS="$FLAGS -msse3"
-fi
 
 if [ "$DEBUG" = "" ]; then
   # Do a build test with debug flags.
   $CC $DIR/gotsan.cpp -c -o $DIR/race_debug_$SUFFIX.syso $DEBUG_FLAGS $CFLAGS
 else
   FLAGS="$DEBUG_FLAGS"
 fi