malloc() call somehow calling the rtld malloc() implementaion

I've been attempting to get OpenOffice to build properly in a
clang400-import poudriere jail and have run into a mystery.  The build
procedure creates a c++ executable "idlc", which is used to build other
stuff.  The new operator has been overrriden to call a custom memory
allocator, which I have configured to call the system version of
malloc().

At some point idlc crashes because it has allocated a 16 byte structure
and the compiler is using "movaps %xmm0,(%rax)" to initialize it, which
requires 16 byte alignment.  Unfortunately this structure is only 8 byte
aligned, causing a bus error.  This shouldn't be happening because our
system malloc() always seems to do the proper alignment.  It appears
that intead of calling the version of malloc() in libc, the simple
version of malloc() built into rtld is being called instead.

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This GDB was configured as "amd64-marcel-freebsd"...
(gdb) break main
Breakpoint 1 at 0x43b1f6: file idlcmain.cxx, line 34.
(gdb) run _at_/tmp/r
Starting program: /wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/bin/idlc _at_/tmp/r
[New LWP 101304]
[New Thread 802616000 (LWP 101304/idlc)]
[Switching to Thread 802616000 (LWP 101304/idlc)]

Breakpoint 1, main (argc=2, argv=0x7fffffffb278) at idlcmain.cxx:34
34	SAL_IMPLEMENT_MAIN_WITH_ARGS(argc, argv)
(gdb) break malloc
Breakpoint 2 at 0x8006a5f01: file /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c, line 163.
(gdb) cont
Continuing.
Trace 12474/1: "Min Prioriy for policy '2' == '0'
"
Trace 12474/1: "Max Prioriy for policy '2' == '103'
"
/wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/bin/idlc: compiling 1 source files ... 
Compiling: /wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/offapi/com/sun/star/i18n/KParseTokens.idl

Breakpoint 2, malloc (nbytes=343)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	/var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c: No such file or directory.
	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
Current language:  auto; currently minimal
(gdb) cont
Continuing.

Breakpoint 2, malloc (nbytes=32)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.
Trace 13112/2: "ChildStatusProc : starting '/wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/bin/ucpp'"
[New Thread 802616500 (LWP 100249/idlc)]
[Switching to Thread 802616500 (LWP 100249/idlc)]

Breakpoint 2, malloc (nbytes=19)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.

Breakpoint 2, malloc (nbytes=34)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.

Breakpoint 2, malloc (nbytes=16)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.

Breakpoint 2, malloc (nbytes=16)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.

Breakpoint 2, malloc (nbytes=16)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.

Breakpoint 2, malloc (nbytes=16)
    at /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c:163
163	in /var/poudriere/jails/clang400amd64/usr/src/libexec/rtld-elf/malloc.c
(gdb) cont
Continuing.
sizeof(AstExprValue)=16

Program received signal SIGBUS, Bus error.
[Switching to Thread 802616000 (LWP 101304/idlc)]
0x0000000000478cc2 in AstExpression::eval_bit_op (this=0x802633dc8, 
    ek=EK_const) at astexpression.cxx:1001
1001	    std::auto_ptr< AstExprValue	> retval(new AstExprValue());


idlc is linked to libc.so:

/wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/bin/idlc:
	libreg.so.3 => /wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/lib/libreg.so.3 (0x8008b9000)
	libuno_sal.so.3 => /wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/lib/libuno_sal.so.3 (0x800c00000)
	libuno_salhelpergcc3.so.3 => /wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/lib/libuno_salhelpergcc3.so.3 (0x801040000)
	libm.so.5 => /lib/libm.so.5 (0x801244000)
	libc++.so.1 => /usr/lib/libc++.so.1 (0x80146e000)
	libcxxrt.so.1 => /lib/libcxxrt.so.1 (0x801735000)
	libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x801953000)
	libthr.so.3 => /lib/libthr.so.3 (0x801b69000)
	libc.so.7 => /lib/libc.so.7 (0x801d91000)
	libstore.so.3 => /wrkdirs/usr/ports/editors/openoffice-devel/work/aoo-4.2.0/main/solver/420/unxfbsdx.pro/lib/libstore.so.3 (0x802152000)


If I create a simple test program that calls malloc() and set a
breakpoint in malloc(), the breakpoint gets set in the rtld version, but
the the libc version of malloc is what gets called.

What the heck is going on here, and how can I fix it?