Some notes on the 'bootstrap with or without libc headers' debate:
http://linuxfromscratch.org/pipermail/lfs-dev/2005-July/052409.html
http://gcc.gnu.org/ml/gcc/2005-07/msg01195.html

--- gcc/config/sh/linux.h
+++ gcc/config/sh/linux.h
@@ -154,6 +154,7 @@
 /* Do code reading to identify a signal frame, and set the frame
    state data appropriately.  See unwind-dw2.c for the structs.  */
 
+#ifndef inhibit_libc
 #ifdef IN_LIBGCC2
 #include <signal.h>
 #include <sys/ucontext.h>
@@ -304,6 +305,7 @@
 
 #endif /* defined (__SH5__) */
 #endif /* IN_LIBGCC2 */
+#endif /* inhibit_libc */
 
 /* For SH3 and SH4, we use a slot of the unwind frame which correspond
    to a fake register number 16 as a placeholder for the return address
--- gcc/config/rs6000/linux.h
+++ gcc/config/rs6000/linux.h
@@ -111,6 +111,7 @@
 /* Do code reading to identify a signal frame, and set the frame
    state data appropriately.  See unwind-dw2.c for the structs.  */
 
+#ifndef inhibit_libc
 #ifdef IN_LIBGCC2
 #include <signal.h>
 
@@ -194,3 +195,4 @@
     (FS)->retaddr_column = CR0_REGNO;					\
     goto SUCCESS;							\
   } while (0)
+#endif /* inhibit_libc */
--- gcc/config/i386/linux.h
+++ gcc/config/i386/linux.h
@@ -218,6 +218,7 @@
 /* Do code reading to identify a signal frame, and set the frame
    state data appropriately.  See unwind-dw2.c for the structs.  */
 
+#ifndef inhibit_libc
 #ifdef IN_LIBGCC2
 /* There's no sys/ucontext.h for some (all?) libc1, so no
    signal-turned-exceptions for them.  There's also no configure-run for
@@ -282,3 +283,4 @@
   } while (0)
 #endif /* not USE_GNULIBC_1 */
 #endif /* IN_LIBGCC2 */
+#endif /* inhibit_libc */
--- gcc/config/alpha/linux.h
+++ gcc/config/alpha/linux.h
@@ -78,6 +78,7 @@
 /* Do code reading to identify a signal frame, and set the frame
    state data appropriately.  See unwind-dw2.c for the structs.  */
 
+#ifndef inhibit_libc
 #ifdef IN_LIBGCC2
 #include <signal.h>
 #include <sys/ucontext.h>
@@ -127,3 +128,4 @@
     (FS)->retaddr_column = 64;						\
     goto SUCCESS;							\
   } while (0)
+#endif /* inhibit_libc */
--- gcc/config/rs6000/linux64.h
+++ gcc/config/rs6000/linux64.h
@@ -561,13 +579,12 @@
 /* Do code reading to identify a signal frame, and set the frame
    state data appropriately.  See unwind-dw2.c for the structs.  */
 
+#ifndef inhibit_libc
 #ifdef IN_LIBGCC2
 #include <signal.h>
 #ifdef __powerpc64__
 #include <sys/ucontext.h>
 
-enum { SIGNAL_FRAMESIZE = 128 };
-
 #else
 
 /* During the 2.5 kernel series the kernel ucontext was changed, but
@@ -581,7 +598,6 @@
   struct sigcontext_struct uc_mcontext;
   sigset_t          uc_sigmask;
 };
-enum { SIGNAL_FRAMESIZE = 64 };
 #endif
 
 #endif
@@ -733,3 +731,9 @@
   } while (0)
 
 #endif
+#endif /* inhibit_libc */
+#ifdef __powerpc64__
+enum { SIGNAL_FRAMESIZE = 128 };
+#else
+enum { SIGNAL_FRAMESIZE = 64 };
+#endif
--- gcc/config.gcc
+++ gcc/config.gcc
@@ -295,7 +295,7 @@
 	need_64bit_hwint=yes
 	;;
 # Note the 'l'; we need to be able to match e.g. "shle" or "shl".
-sh[123456789l]*-*-*)
+sh[123456789lbe]*-*-*)
 	cpu_type=sh
 	need_64bit_hwint=yes
 	;;