Keep original file if -c or --stdout is given

Set removeSrcFile back to false when -c or --stdout is used to improve
compatibility with gzip(1) behavior.

gzip(1) is removing the original file on compression unless --stdout or
/-c is used. zstd is defaulting to keep the file unless --rm is used or
when it is called via a gzip symlink, in which it is removing by
default. Specifying -c/--stdout turns this behavior off.

tests/cli-tests/compression/basic.sh

@@ -24,6 +24,10 @@ zstd -c file       | zstd -t
 zstd --stdout file | zstd -t
 println bob | zstd | zstd -t
 
+# Test keeping input file when compressing to stdout in gzip mode
+$ZSTD_SYMLINK_DIR/gzip -c file       | zstd -t ; test -f file
+$ZSTD_SYMLINK_DIR/gzip --stdout file | zstd -t ; test -f file
+
 # Test --rm
 cp file file-rm
 zstd --rm file-rm; zstd -t file-rm.zst