PR ld/20828: Relax symbol ordering in tests
    
    Complement commit 81ff47b3a546 ("PR ld/20828: Fix linker script symbols
    wrongly forced local with section GC") and make tests check for the
    presence of global `_fdata' and `_edata' symbols separately, removing
    any dependency on symbol table ordering for tests to succeed and
    removing:
    
    FAIL: PR ld/20828 dynamic symbols with section GC (auxiliary shared library)
    FAIL: PR ld/20828 dynamic symbols with section GC (plain)
    
    failures with the `x86_64-solaris2' target, which has additional
    intervening entries:
    
    Symbol table '.dynsym' contains 6 entries:
       Num:    Value          Size Type    Bind   Vis      Ndx Name
         0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
         1: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT    1 _fdata
         2: 0000000000000000     0 OBJECT  GLOBAL DEFAULT    1 _DYNAMIC
         3: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS _PROCEDURE_LINKAGE_TABLE_
         4: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT    1 _edata
         5: 00000000000001b8     0 OBJECT  GLOBAL DEFAULT    4 _GLOBAL_OFFSET_TABLE_
    
    Rename dump pattern files accordingly for consistency.
    
    	ld/
    	PR ld/20828
    	* testsuite/ld-elf/pr20828-1.sd: Remove test.
    	* testsuite/ld-elf/pr20828-a.sd: New test.
    	* testsuite/ld-elf/pr20828-2a.sd: Rename test to...
    	* testsuite/ld-elf/pr20828-b.sd: ... this.
    	* testsuite/ld-elf/pr20828-2b.sd: Rename test to...
    	* testsuite/ld-elf/pr20828-c.sd: ... this.
    	* testsuite/ld-elf/shared.exp: Adjust accordingly.
    
    (cherry picked from commit adcbdc63e5ccf663dacc8493cec63a95b653285e)