[gcc r14-4878] libgcc: make heap-based trampolines conditional on libc presence

[Sergei Trofimovich <slyfox@gcc.gnu.org>]

https://gcc.gnu.org/g:eaf75155f38a51b2d9d49c6c1b1e1639e3d0591a

commit r14-4878-geaf75155f38a51b2d9d49c6c1b1e1639e3d0591a
Author: Sergei Trofimovich <siarheit@google.com>
Date:   Mon Oct 23 13:32:55 2023 +0100

    libgcc: make heap-based trampolines conditional on libc presence
    
    To build `libc` for a target one needs to build `gcc` without `libc`
    support first. Commit r14-4823-g8abddb187b3348 "libgcc: support
    heap-based trampolines" added unconditional `libc` dependency and broke
    libc-less `gcc` builds.
    
    An example failure on `x86_64-unknown-linux-gnu`:
    
        $ mkdir -p /tmp/empty
        $ ../gcc/configure \
            --disable-multilib \
            --without-headers \
            --with-newlib \
            --enable-languages=c \
            --disable-bootstrap \
            --disable-gcov \
            --disable-threads \
            --disable-shared \
            --disable-libssp \
            --disable-libquadmath \
            --disable-libgomp \
            --disable-libatomic \
            --with-build-sysroot=/tmp/empty
        $ make
        ...
        /tmp/gb/./gcc/xgcc -B/tmp/gb/./gcc/ -B/usr/local/x86_64-pc-linux-gnu/bin/ -B/usr/local/x86_64-pc-linux-gnu/lib/ -isystem /usr/local/x86_64-pc-linux-gnu/include -isystem /usr/local/x86_64-pc-linux-gnu/sys-include --sysroot=/tmp/empty   -g -O2 -O2  -g -O2 -DIN_GCC   -W -Wall -Wno-narrowing -Wwrite-strings -Wcast-qual -Wstrict-prototypes -Wmissing-prototypes -Wold-style-definition  -isystem ./include  -fpic -mlong-double-80 -DUSE_ELF_SYMVER -fcf-protection -mshstk -g -DIN_LIBGCC2 -fbuilding-libgcc -fno-stack-protector -Dinhibit_libc -fpic -mlong-double-80 -DUSE_ELF_SYMVER -fcf-protection -mshstk -I. -I. -I../.././gcc -I/home/slyfox/dev/git/gcc/libgcc -I/home/slyfox/dev/git/gcc/libgcc/. -I/home/slyfox/dev/git/gcc/libgcc/../gcc -I/home/slyfox/dev/git/gcc/libgcc/../include  -DHAVE_CC_TLS  -DUSE_TLS  -o heap-trampoline.o -MT heap-trampoline.o -MD -MP -MF heap-trampoline.dep  -c .../gcc/libgcc/config/i386/heap-trampoline.c -fvisibility=hidden -DHIDE_EXPORTS
        ../gcc/libgcc/config/i386/heap-trampoline.c:3:10: fatal error: unistd.h: No such file or directory
            3 | #include <unistd.h>
              |          ^~~~~~~~~~
        compilation terminated.
        make[2]: *** [.../gcc/libgcc/static-object.mk:17: heap-trampoline.o] Error 1
        make[2]: Leaving directory '/tmp/gb/x86_64-pc-linux-gnu/libgcc'
        make[1]: *** [Makefile:13307: all-target-libgcc] Error 2
    
    The change inhibits any heap-based trampoline code.
    
    libgcc/
    
            * config/aarch64/heap-trampoline.c: Disable when libc is not
            present.
            * config/i386/heap-trampoline.c: Ditto.

Diff:
---
 libgcc/config/aarch64/heap-trampoline.c | 5 +++++
 libgcc/config/i386/heap-trampoline.c    | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/libgcc/config/aarch64/heap-trampoline.c b/libgcc/config/aarch64/heap-trampoline.c
index c8b83681ed7e..f22233987ca5 100644
--- a/libgcc/config/aarch64/heap-trampoline.c
+++ b/libgcc/config/aarch64/heap-trampoline.c
@@ -1,5 +1,8 @@
 /* Copyright The GNU Toolchain Authors. */
 
+/* libc is required to allocate trampolines.  */
+#ifndef inhibit_libc
+
 #include <unistd.h>
 #include <sys/mman.h>
 #include <stdint.h>
@@ -170,3 +173,5 @@ __builtin_nested_func_ptr_deleted (void)
       tramp_ctrl_curr = prev;
     }
 }
+
+#endif /* !inhibit_libc */
diff --git a/libgcc/config/i386/heap-trampoline.c b/libgcc/config/i386/heap-trampoline.c
index 96e13bf828ea..4b9f43658689 100644
--- a/libgcc/config/i386/heap-trampoline.c
+++ b/libgcc/config/i386/heap-trampoline.c
@@ -1,5 +1,8 @@
 /* Copyright The GNU Toolchain Authors. */
 
+/* libc is required to allocate trampolines.  */
+#ifndef inhibit_libc
+
 #include <unistd.h>
 #include <sys/mman.h>
 #include <stdint.h>
@@ -170,3 +173,5 @@ __builtin_nested_func_ptr_deleted (void)
       tramp_ctrl_curr = prev;
     }
 }
+
+#endif /* !inhibit_libc */