gcc: Support Canadian cross builds on microblazeel

Picolibc uses the linker during the build process to construct crt0.o
files, but the microblazeel spec from gcc adds -dT xilinx.ld when no
-T argument is provided to introduce default linking
parameters. However, during a Canadian cross build, the xilinx.ld file
isn't installed before picolibc gets built causing the build to fail.

Fix this by making the presence of the xilinx.ld file optional; if it
isn't available, then don't use it. This took two checks as the spec
file conditionals can only insert a single argument and we need two,
the -dT and the full path to the script.

Signed-off-by: Keith Packard <[email protected]>

Author: keith-packard

gcc/config/microblaze/microblaze.h

@@ -115,7 +115,7 @@ extern enum pipeline_type microblaze_pipe;
   %{Zxl-mode-xmdstub:-defsym _TEXT_START_ADDR=0x800} \
   %{mxl-mode-xmdstub:-defsym _TEXT_START_ADDR=0x800} \
   %{mxl-gp-opt:%{G*}} %{!mxl-gp-opt: -G 0} \
-  %{!T*: -dT xilinx.ld%s}"
+  %{!T*: %:if-exists-then-else(xilinx.ld%s -dT) %:if-exists(xilinx.ld%s)}"
 
 /* Specs for the compiler proper  */