man[13]/*: ffix: change '--' to '\-\-' (options) or '\(em' (em-dash)

Change '--' to '\-\-' for options and '--' between words to '\(em'
(em-dash).

Signed-off-by: Bjarni Ingi Gislason <bjarniig@rhi.hi.is>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man1/memusagestat.1

@@ -33,7 +33,7 @@ memory profiling data in the file
 that file is generated via the
 .I \-d
 (or
-.IR --data )
+.IR \-\-data )
 option of
 .BR memusage (1).
 .PP

man3/dlsym.3

@@ -145,7 +145,7 @@ function is a GNU extension.
 There are several scenarios when the address of a global symbol is NULL.
 For example, a symbol can be placed at zero address by the linker, via
 a linker script or with
-.I --defsym
+.I \-\-defsym
 command-line option. Undefined weak symbols also have NULL value.
 Finally, the symbol value may be the result of
 a GNU indirect function (IFUNC) resolver function that returns

man3/posix_spawn.3

@@ -430,7 +430,7 @@ If
 .I file_actions
 is NULL, then no special action is taken, and standard
 .BR exec (3)
-semantics apply--file descriptors open before the exec
+semantics apply\(emfile descriptors open before the exec
 remain open in the new process,
 except those for which the
 .B FD_CLOEXEC