move signal.h REG_* macros under _GNU_SOURCE protection

they were accidentally exposed under just baseline POSIX, which is a
big namespace pollution issue. thankfully glibc only exposes them
under _GNU_SOURCE, not under any of its other options, so omitting
the pollution in the default _BSD_SOURCE profile does not hurt
application compatibility at all.

arch/i386/bits/signal.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 
+#ifdef _GNU_SOURCE
+#define REG_GS          0
+#define REG_FS          1
+#define REG_ES          2
+#define REG_DS          3
+#define REG_EDI         4
+#define REG_ESI         5
+#define REG_EBP         6
+#define REG_ESP         7
+#define REG_EBX         8
+#define REG_EDX         9
+#define REG_ECX         10
+#define REG_EAX         11
+#define REG_TRAPNO      12
+#define REG_ERR         13
+#define REG_EIP         14
+#define REG_CS          15
+#define REG_EFL         16
+#define REG_UESP        17
+#define REG_SS          18
+#endif
+
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 typedef int greg_t, gregset_t[19];
 typedef struct _fpstate {
@@ -49,26 +71,6 @@ typedef struct __ucontext {
 #define SA_RESETHAND  0x80000000
 #define SA_RESTORER   0x04000000
 
-#define REG_GS		0
-#define REG_FS		1
-#define REG_ES		2
-#define REG_DS		3
-#define REG_EDI		4
-#define REG_ESI		5
-#define REG_EBP		6
-#define REG_ESP		7
-#define REG_EBX		8
-#define REG_EDX		9
-#define REG_ECX		10
-#define REG_EAX		11
-#define REG_TRAPNO	12
-#define REG_ERR		13
-#define REG_EIP		14
-#define REG_CS		15
-#define REG_EFL		16
-#define REG_UESP	17
-#define REG_SS		18
-
 #endif
 
 #define SIGHUP    1

arch/x86_64/bits/signal.h

 #if defined(_POSIX_SOURCE) || defined(_POSIX_C_SOURCE) \
  || defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 
+#ifdef _GNU_SOURCE
+#define REG_R8          0
+#define REG_R9          1
+#define REG_R10         2
+#define REG_R11         3
+#define REG_R12         4
+#define REG_R13         5
+#define REG_R14         6
+#define REG_R15         7
+#define REG_RDI         8
+#define REG_RSI         9
+#define REG_RBP         10
+#define REG_RBX         11
+#define REG_RDX         12
+#define REG_RAX         13
+#define REG_RCX         14
+#define REG_RSP         15
+#define REG_RIP         16
+#define REG_EFL         17
+#define REG_CSGFS       18
+#define REG_ERR         19
+#define REG_TRAPNO      20
+#define REG_OLDMASK     21
+#define REG_CR2         22
+#endif
+
 #if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 typedef long long greg_t, gregset_t[23];
 typedef struct _fpstate {
@@ -52,30 +78,6 @@ typedef struct __ucontext {
 #define SA_RESETHAND  0x80000000
 #define SA_RESTORER   0x04000000
 
-#define REG_R8		0
-#define REG_R9		1
-#define REG_R10		2
-#define REG_R11		3
-#define REG_R12		4
-#define REG_R13		5
-#define REG_R14		6
-#define REG_R15		7
-#define REG_RDI		8
-#define REG_RSI		9
-#define REG_RBP		10
-#define REG_RBX		11
-#define REG_RDX		12
-#define REG_RAX		13
-#define REG_RCX		14
-#define REG_RSP		15
-#define REG_RIP		16
-#define REG_EFL		17
-#define REG_CSGFS	18
-#define REG_ERR		19
-#define REG_TRAPNO	20
-#define REG_OLDMASK	21
-#define REG_CR2		22
-
 #endif
 
 #define SIGHUP    1