[ELF] - Implemented --section-start, -Ttext, -Tdata, -Tbss options.

--section-start=sectionname=org
Locate a section in the output file at the absolute address given by org. 
You may use this option as many times as necessary to locate multiple sections in the command line.
 org must be a single hexadecimal integer; for compatibility with other linkers, 
you may omit the leading `0x' usually associated with hexadecimal values. 
Note: there should be no white space between sectionname, the equals sign (“<=>”), and org.

-Tbss=org
-Tdata=org
-Ttext=org
Same as --section-start, with .bss, .data or .text as the sectionname.

Differential revision: https://reviews.llvm.org/D24294

llvm-svn: 281458