Fix --brute for p_lx_elf.cpp, which compresses multiple pieces

Force all pieces to use the same de-compressor.
(Future: allow each PT_LOAD to choose its own.)
Has minor wobbles due to page alignment, and size of de-compressor.
64-bit only for now.
https://github.com/upx/upx/issues/570
https://github.com/upx/upx/issues/297
	modified:   p_lx_elf.cpp
	modified:   p_unix.cpp
	modified:   packer.cpp
	modified:   packer.h

src/p_unix.cpp

@@ -394,7 +394,7 @@ void PackUnix::packExtent(
             MemBuffer hdr_obuf;
             hdr_obuf.allocForCompression(hdr_u_len);
             int r = upx_compress(hdr_ibuf, hdr_u_len, hdr_obuf, &hdr_c_len, nullptr,
-                ph.method, 10, nullptr, nullptr);
+                forced_method(ph.method), 10, nullptr, nullptr);
             if (r != UPX_E_OK)
                 throwInternalError("header compression failed");
             if (hdr_c_len >= hdr_u_len)
@@ -407,7 +407,7 @@ void PackUnix::packExtent(
             memset(&tmp, 0, sizeof(tmp));
             set_te32(&tmp.sz_unc, hdr_u_len);
             set_te32(&tmp.sz_cpr, hdr_c_len);
-            tmp.b_method = (unsigned char) ph.method;
+            tmp.b_method = (unsigned char) forced_method(ph.method);
             tmp.b_extra = b_extra;
             fo->write(&tmp, sizeof(tmp));
             b_len += sizeof(b_info);