[gdb/testsuite] Fix gdb.reverse/solib-{precsave,reverse}.exp with gcc-8

[gdb/testsuite] Fix gdb.reverse/solib-{precsave,reverse}.exp with gcc-8

With gcc-8, we have the following FAILs, which are not there for gcc-7:
...
FAIL: gdb.reverse/solib-precsave.exp: reverse-step into solib function one
FAIL: gdb.reverse/solib-precsave.exp: reverse-step within solib function one
FAIL: gdb.reverse/solib-precsave.exp: reverse-step back to main one
FAIL: gdb.reverse/solib-precsave.exp: reverse-step into solib function two
FAIL: gdb.reverse/solib-precsave.exp: reverse-step within solib function two
FAIL: gdb.reverse/solib-precsave.exp: reverse-step back to main two
FAIL: gdb.reverse/solib-precsave.exp: run until end part two
FAIL: gdb.reverse/solib-precsave.exp: reverse-next over solib function one
FAIL: gdb.reverse/solib-reverse.exp: reverse-step into solib function one
FAIL: gdb.reverse/solib-reverse.exp: reverse-step within solib function one
FAIL: gdb.reverse/solib-reverse.exp: reverse-step back to main one
FAIL: gdb.reverse/solib-reverse.exp: reverse-step into solib function two
FAIL: gdb.reverse/solib-reverse.exp: reverse-step within solib function two
FAIL: gdb.reverse/solib-reverse.exp: reverse-step back to main two
FAIL: gdb.reverse/solib-reverse.exp: run until end part two
FAIL: gdb.reverse/solib-reverse.exp: reverse-next over solib function one
...

Looking at the first FAIL for gdb.reverse/solib-precsave.exp, we have:
...
 (gdb) PASS: reverse-next first shr1
 reverse-next^M
 40        b[0] = 6;   b[1] = 9;     /* generic statement, end part two */^M
 (gdb) PASS: reverse-next generic
 reverse-step^M
-shr2 (x=17) at gdb.reverse/shr2.c:23^M
-23      }^M
-(gdb) PASS: reverse-step into solib function one
+38        b[1] = shr2(17);              /* middle part two */^M
+(gdb) FAIL: reverse-step into solib function one
...

There's a difference in line number info for line 38, where for gcc-7 we have:
...
Line number    Starting address    View    Stmt
         38            0x4005c6               x
...
and for gcc-8:
...
         38            0x4005c1               x
         38            0x4005cb               x
...
which explains why we don't step directly into "solib function one".

Fix this by recognizing the extra "recommended breakpoint location" and
issuing an additional reverse-next/step.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-07-21  Tom de Vries  <tdevries@suse.de>

	* gdb.reverse/solib-precsave.exp: Handle additional "recommended
	breakpoint locations".
	* gdb.reverse/solib-reverse.exp: Same.