Many changes for ELF shared libraries on Linux and Android

Handling more than 2 PT_LOAD (and thus more than 1 executable PT_LOAD)
required extensive changes.  But the bonus is the infrastructure
to support a different (de-)compression algorithm for each PT_LOAD.

https://github.com/upx/upx/issues/341   i386 .so decompression
https://github.com/upx/upx/issues/609   armv7 .so on Android
https://github.com/upx/upx/issues/625   amd64 .so execution
https://github.com/upx/upx/issues/654   armv7 .exe
Not yet: .so on MIPS, PowerPC, PowerPC64

src/stub/tmp/armeb.v4a-linux.elf-entry.bin.dump

@@ -113,6 +113,7 @@ OFFSET   TYPE              VALUE
 00000008 R_ARM_PC24        LZMA_ELF00
 0000004c R_ARM_PC24        LZMA_ELF00
 00000080 R_ARM_PC24        LZMA_ELF00
+000000a8 R_ARM_PC24        LZMA_ELF00
 
 RELOCATION RECORDS FOR [LZMA_DEC20]:
 OFFSET   TYPE              VALUE