[build] Apply the "-fno-PIE -nopie" workaround only to i386 builds

Hardened versions of gcc default to building position-independent
code, which breaks our i386 build.  Our build process therefore
detects such platforms and automatically adds "-fno-PIE -nopie" to the
gcc command line.

On x86_64, we choose to build position-independent code (in order to
reduce the final binary size and, in particular, the number of
relocations required for UEFI binaries).  The workaround therefore
breaks the build process for x86_64 binaries on such platforms.

Fix by moving the workaround to the i386-specific portion of the
Makefile.

Reported-by: Jan Kundrát <jkt@kde.org>
Debugged-by: Jan Kundrát <jkt@kde.org>
Debugged-by: Marin Hannache <git@mareo.fr>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/Makefile.housekeeping

 WORKAROUND_CFLAGS += $(SP_FLAGS)
 endif
 
-# Some widespread patched versions of gcc include -fPIE -Wl,-pie by
-# default.  Note that gcc will exit *successfully* if it fails to
-# recognise an option that starts with "no", so we have to test for
-# output on stderr instead of checking the exit status.
-#
-ifeq ($(CCTYPE),gcc)
-PIE_TEST = [ -z "`$(CC) -fno-PIE -nopie -x c -c /dev/null -o /dev/null 2>&1`" ]
-PIE_FLAGS := $(shell $(PIE_TEST) && $(ECHO) '-fno-PIE -nopie')
-WORKAROUND_CFLAGS += $(PIE_FLAGS)
-endif
-
 # gcc 4.4 generates .eh_frame sections by default, which distort the
 # output of "size".  Inhibit this.
 #

src/arch/i386/Makefile

 #
 CFLAGS			+= -Ui386
 
+# Some widespread patched versions of gcc include -fPIE -Wl,-pie by
+# default.  Note that gcc will exit *successfully* if it fails to
+# recognise an option that starts with "no", so we have to test for
+# output on stderr instead of checking the exit status.
+#
+ifeq ($(CCTYPE),gcc)
+PIE_TEST = [ -z "`$(CC) -fno-PIE -nopie -x c -c /dev/null -o /dev/null 2>&1`" ]
+PIE_FLAGS := $(shell $(PIE_TEST) && $(ECHO) '-fno-PIE -nopie')
+WORKAROUND_CFLAGS += $(PIE_FLAGS)
+endif
+
 # Define version string for lkrnprefix.S
 #
 CFLAGS_lkrnprefix	+= -DVERSION="\"$(VERSION)\""