build: fix header files for Plan 9

The "elf.h" header changes involve only comments, the released
Plan 9 C preprocessing function does not cope with multiline
comments following the #define keyword.  All multiline comments
have been moved to the line above the associated definition.
Sigh!  Fixing the Plan 9 compiler is not an option.

<time.h> does not exist in the Plan 9 Native library.  I have
moved it from src/cmd/ld/pe.h to include/u.h. RSC correctly points
out that this copy of <u.h> is not the one used to compile the
Go release on Plan 9 platforms.

R=golang-dev
CC=golang-dev, rsc
https://golang.org/cl/4574042

include/u.h

@@ -69,6 +69,7 @@ extern "C" {
 #include <math.h>
 #include <ctype.h>	/* for tolower */
 #include <signal.h>
+#include <time.h>
 
 /*
  * OS-specific crap

src/cmd/ld/elf.h

@@ -262,8 +262,8 @@ typedef struct {
 
 /* Values for d_tag. */
 #define DT_NULL		0	/* Terminating entry. */
-#define DT_NEEDED	1	/* String table offset of a needed shared
-				   library. */
+/* String table offset of a needed shared library. */
+#define DT_NEEDED	1
 #define DT_PLTRELSZ	2	/* Total size in bytes of PLT relocations. */
 #define DT_PLTGOT	3	/* Processor-dependent address. */
 #define DT_HASH		4	/* Address of symbol hash table. */
@@ -276,8 +276,8 @@ typedef struct {
 #define DT_SYMENT	11	/* Size of each symbol table entry. */
 #define DT_INIT		12	/* Address of initialization function. */
 #define DT_FINI		13	/* Address of finalization function. */
-#define DT_SONAME	14	/* String table offset of shared object
-				   name. */
+/* String table offset of shared object name. */
+#define DT_SONAME	14
 #define DT_RPATH	15	/* String table offset of library path. [sup] */
 #define DT_SYMBOLIC	16	/* Indicates "symbolic" linking. [sup] */
 #define DT_REL		17	/* Address of ElfNN_Rel relocations. */
@@ -285,30 +285,29 @@ typedef struct {
 #define DT_RELENT	19	/* Size of each ElfNN_Rel relocation. */
 #define DT_PLTREL	20	/* Type of relocation used for PLT. */
 #define DT_DEBUG	21	/* Reserved (not used). */
-#define DT_TEXTREL	22	/* Indicates there may be relocations in
-				   non-writable segments. [sup] */
+/* Indicates there may be relocations in non-writable segments. [sup] */
+#define DT_TEXTREL	22
 #define DT_JMPREL	23	/* Address of PLT relocations. */
 #define	DT_BIND_NOW	24	/* [sup] */
-#define	DT_INIT_ARRAY	25	/* Address of the array of pointers to
-				   initialization functions */
-#define	DT_FINI_ARRAY	26	/* Address of the array of pointers to
-				   termination functions */
-#define	DT_INIT_ARRAYSZ	27	/* Size in bytes of the array of
-				   initialization functions. */
-#define	DT_FINI_ARRAYSZ	28	/* Size in bytes of the array of
-				   terminationfunctions. */
-#define	DT_RUNPATH	29	/* String table offset of a null-terminated
-				   library search path string. */
+/* Address of the array of pointers to initialization functions */
+#define	DT_INIT_ARRAY	25
+/* Address of the array of pointers to termination functions */
+#define	DT_FINI_ARRAY	26
+/* Size in bytes of the array of initialization functions. */
+#define	DT_INIT_ARRAYSZ	27
+/* Size in bytes of the array of terminationfunctions. */
+#define	DT_FINI_ARRAYSZ	28
+/* String table offset of a null-terminated library search path string. */
+#define	DT_RUNPATH	29
 #define	DT_FLAGS	30	/* Object specific flag values. */
-#define	DT_ENCODING	32	/* Values greater than or equal to DT_ENCODING
-				   and less than DT_LOOS follow the rules for
-				   the interpretation of the d_un union
-				   as follows: even == 'd_ptr', even == 'd_val'
-				   or none */
-#define	DT_PREINIT_ARRAY 32	/* Address of the array of pointers to
-				   pre-initialization functions. */
-#define	DT_PREINIT_ARRAYSZ 33	/* Size in bytes of the array of
-				   pre-initialization functions. */
+/*	Values greater than or equal to DT_ENCODING and less than
+	DT_LOOS follow the rules for the interpretation of the d_un
+	union as follows: even == 'd_ptr', even == 'd_val' or none */
+#define	DT_ENCODING	32
+/* Address of the array of pointers to pre-initialization functions. */
+#define	DT_PREINIT_ARRAY 32
+/* Size in bytes of the array of pre-initialization functions. */
+#define	DT_PREINIT_ARRAYSZ 33
 #define	DT_LOOS		0x6000000d	/* First OS-specific */
 #define	DT_HIOS		0x6ffff000	/* Last OS-specific */
 #define	DT_LOPROC	0x70000000	/* First processor-specific type. */
@@ -319,19 +318,19 @@ typedef struct {
 #define	DT_VERSYM	0x6ffffff0
 
 /* Values for DT_FLAGS */
-#define	DF_ORIGIN	0x0001	/* Indicates that the object being loaded may
-				   make reference to the $ORIGIN substitution
-				   string */
+/*	Indicates that the object being loaded may make reference to
+	the $ORIGIN substitution string */
+#define	DF_ORIGIN	0x0001
 #define	DF_SYMBOLIC	0x0002	/* Indicates "symbolic" linking. */
-#define	DF_TEXTREL	0x0004	/* Indicates there may be relocations in
-				   non-writable segments. */
-#define	DF_BIND_NOW	0x0008	/* Indicates that the dynamic linker should
-				   process all relocations for the object
-				   containing this entry before transferring
-				   control to the program. */
-#define	DF_STATIC_TLS	0x0010	/* Indicates that the shared object or
-				   executable contains code using a static
-				   thread-local storage scheme. */
+/* Indicates there may be relocations in non-writable segments. */
+#define	DF_TEXTREL	0x0004
+/*	Indicates that the dynamic linker should process all
+	relocations for the object containing this entry before
+	transferring control to the program.  */
+#define	DF_BIND_NOW	0x0008
+/*	Indicates that the shared object or executable contains code
+	using a static thread-local storage scheme.  */
+#define	DF_STATIC_TLS	0x0010
 
 /* Values for n_type.  Used in core files. */
 #define NT_PRSTATUS	1	/* Process status. */