CI: coverity: simplify debugging options

We used to rely on a call to "sed" to modify the DEBUG option in the
makefile when running under Coverity because it splits words around
spaces and does not allow to pass multi-word build options. As reported
by Tim in issue #1592, this broke with commit 8de7f2822 ("BUILD: makefile:
enable both DEBUG_STRICT and DEBUG_MEMORY_POOLS by default") when the
default DEBUG options changed.

Let's change this to pass all DEBUG options one at a time instead and
get rid of this sed.
diff --git a/.github/workflows/coverity.yml b/.github/workflows/coverity.yml
index cfde87b..0c4b2d0 100644
--- a/.github/workflows/coverity.yml
+++ b/.github/workflows/coverity.yml
@@ -20,7 +20,9 @@
       COVERITY_SCAN_PROJECT_NAME: 'Haproxy'
       COVERITY_SCAN_BRANCH_PATTERN: '*'
       COVERITY_SCAN_NOTIFICATION_EMAIL: 'chipitsine@gmail.com'
-      COVERITY_SCAN_BUILD_COMMAND: "make CC=clang TARGET=linux-glibc USE_ZLIB=1 USE_PCRE=1 USE_PCRE_JIT=1 USE_LUA=1 USE_OPENSSL=1 USE_QUIC=1 USE_SYSTEMD=1 USE_WURFL=1 WURFL_INC=addons/wurfl/dummy WURFL_LIB=addons/wurfl/dummy USE_DEVICEATLAS=1 DEVICEATLAS_SRC=addons/deviceatlas/dummy USE_51DEGREES=1 51DEGREES_SRC=addons/51degrees/dummy/pattern ADDLIB=\"-Wl,-rpath,$HOME/opt/lib/\" SSL_LIB=${HOME}/opt/lib SSL_INC=${HOME}/opt/include"
+      # We cannot pass the DEBUG at once here because Coverity splits
+      # parameters at whitespaces, without taking quoting into account.
+      COVERITY_SCAN_BUILD_COMMAND: "make CC=clang TARGET=linux-glibc USE_ZLIB=1 USE_PCRE=1 USE_PCRE_JIT=1 USE_LUA=1 USE_OPENSSL=1 USE_QUIC=1 USE_SYSTEMD=1 USE_WURFL=1 WURFL_INC=addons/wurfl/dummy WURFL_LIB=addons/wurfl/dummy USE_DEVICEATLAS=1 DEVICEATLAS_SRC=addons/deviceatlas/dummy USE_51DEGREES=1 51DEGREES_SRC=addons/51degrees/dummy/pattern ADDLIB=\"-Wl,-rpath,$HOME/opt/lib/\" SSL_LIB=${HOME}/opt/lib SSL_INC=${HOME}/opt/include DEBUG+=-DDEBUG_STRICT=1 DEBUG+=-DDEBUG_USE_ABORT=1"
     steps:
     - uses: actions/checkout@v2
     - name: Install apt dependencies
@@ -32,12 +34,6 @@
     - name: Install QUICTLS
       run: |
         QUICTLS=yes scripts/build-ssl.sh
-    - name: Hijack Makefile
-      run: |
-        # We cannot pass the DEBUG variable in `COVERITY_SCAN_BUILD_COMMAND`,
-        # because Coverity splits parameters at whitespaces, without taking
-        # quoting into account.
-        sed -i 's/^DEBUG =$/DEBUG = -DDEBUG_STRICT=1 -DDEBUG_USE_ABORT=1/' Makefile
     - name: Build WURFL
       run: make -C addons/wurfl/dummy
     - name: Run Coverity Scan