Taken from
https://sources.debian.net/data/main/g/gcc-4.9/4.9.2-10/debian/patches/gcj-arm-mode.diff

# DP: For armhf, force arm mode instead of thumb mode

--- a/libjava/configure.host
+++ b/libjava/configure.host
@@ -66,6 +66,9 @@
     ;;
 esac
 
+# on armhf force arm mode
+libgcj_flags="${libgcj_flags} -marm"
+
 AM_RUNTESTFLAGS= 
 
 # Set any host dependent compiler flags.
--- a/gcc/java/lang-specs.h
+++ b/gcc/java/lang-specs.h
@@ -47,7 +47,7 @@
     %{.class|.zip|.jar|!fsyntax-only:jc1				\
       %{.java|fsaw-java-file:%U.jar -fsource-filename=%i %<ffilelist-file} \
       %{.class|.zip|.jar|ffilelist-file|fcompile-resource*:%i}		\
-      %(jc1) %(cc1_options) %{I*} %{!findirect-dispatch:-faux-classpath %U.zip} \
+      %(jc1) %(cc1_options) -marm %{I*} %{!findirect-dispatch:-faux-classpath %U.zip} \
       %{MD:-MD_} %{MMD:-MMD_} %{M} %{MM} %{MA} %{MT*} %{MF*}\
       %(invoke_as)}",
       0, 0, 0},
--- a/libjava/libgcj.spec.in
+++ b/libjava/libgcj.spec.in
@@ -9,4 +9,4 @@
 %rename lib liborig
 *lib: @LD_START_STATIC_SPEC@ @LIBGCJ_SPEC@ @LD_FINISH_STATIC_SPEC@ @LIBMATHSPEC@ @LDLIBICONV@ @GCSPEC@ @THREADSPEC@ @ZLIBSPEC@ @SYSTEMSPEC@ %(libgcc) @LIBSTDCXXSPEC@ %(liborig)
 
-*jc1: @HASH_SYNC_SPEC@ @DIVIDESPEC@ @CHECKREFSPEC@ @JC1GCSPEC@ @EXCEPTIONSPEC@ @BACKTRACESPEC@ @IEEESPEC@ @ATOMICSPEC@ @LIBGCJ_BC_SPEC@ -fkeep-inline-functions
+*jc1: @HASH_SYNC_SPEC@ @DIVIDESPEC@ @CHECKREFSPEC@ @JC1GCSPEC@ @EXCEPTIONSPEC@ @BACKTRACESPEC@ @IEEESPEC@ @ATOMICSPEC@ @LIBGCJ_BC_SPEC@ -fkeep-inline-functions -marm