tsan: add pragma line to buildgo.sh

Add pragma line so that errors messages point to the actual
source files rather than to the concatenated gotsan.cpp.

Reviewed By: vitalybuka, melver

Differential Revision: https://reviews.llvm.org/D106275

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

@@ -170,11 +170,10 @@ else
 fi
 
 SRCS="$SRCS $ADD_SRCS"
-
-rm -f $DIR/gotsan.cpp
 for F in $SRCS; do
-	cat $F >> $DIR/gotsan.cpp
-done
+	echo "#line 1 \"$F\""
+	cat $F
+done > $DIR/gotsan.cpp
 
 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"