Ignore *.o everywhere

We don't commit *.o files anywhere, not even as test data. So ignore them
everywhere.

Also remove a redundant ignore of *.exe in a subdirectory.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/.gitignore b/.gitignore
index 6a3221c..af52c64 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,6 +28,9 @@
 .project
 /.settings
 
+# Unix-like build artifacts:
+*.o
+
 # MSVC build artifacts:
 *.exe
 *.pdb
diff --git a/3rdparty/everest/.gitignore b/3rdparty/everest/.gitignore
index 6eb25f6..f3c7a7c 100644
--- a/3rdparty/everest/.gitignore
+++ b/3rdparty/everest/.gitignore
@@ -1,2 +1 @@
-*.o
 Makefile
diff --git a/library/.gitignore b/library/.gitignore
index 3a63a63..9aa6322 100644
--- a/library/.gitignore
+++ b/library/.gitignore
@@ -1,4 +1,3 @@
-*.o
 libmbed*
 *.sln
 *.vcxproj
diff --git a/programs/.gitignore b/programs/.gitignore
index d402607..59634b5 100644
--- a/programs/.gitignore
+++ b/programs/.gitignore
@@ -5,9 +5,6 @@
 *.sln
 *.vcxproj
 
-*.o
-*.exe
-
 aes/crypt_and_hash
 hash/generic_sum
 hash/hello
diff --git a/tests/.gitignore b/tests/.gitignore
index 07ac5d6..4678d8d 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -10,9 +10,6 @@
 
 include/test/instrument_record_status.h
 
-src/*.o
-src/test_helpers/*.o
-src/drivers/*.o
 src/libmbed*
 
 libtestdriver1/*